• Tunnel and Underground Space
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• v.13 no.4
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• pp.304-315
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• 2003

In this paper, the DDA method with a new hydro-mechanical algorithm is used to study the effect of rock discontinuities on uplift and seepage in concrete gravity dam foundations. This paper presents an alternative method of predicting uplift and seepage at the base of concrete gravity dams. A sensitivity analysis was carried out to study the importance of several parameters on dam stability such as the orientation, spacing, and location of discontinuities. The study shows that joint water flow and adverse geological conditions could result in unusual uplift at the base of concrete gravity dams, well in excess of what is predicted with the classical linear or hi-linear pressure assumption. It is shown that, in general, the DDA program with the hydro-mechanical algorithm can be used as a practical tool in the design of gravity dams built on fractured rock masses.

• Explosives and Blasting
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• v.30 no.1
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• pp.29-36
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• 2012

In this study, the influence of priming location inside a blast hole on the ground vibration has been studied. In most of the previous studies dealing with the ground vibration, the effect of priming location in a blast hole was usually considered in a limited way. Thus, it seems that the results of the studies can be applicable only to the relevant sites. Considering the fact that the mechanism of ground vibration caused by blasting is quite complex, the priming location can have a considerable effect on the ground vibration in certain situations and be an important parameter in a blasting design. To identify the characteristics of the wave propagation according to priming locations, total 72 test blasts were carried out with different spacing, burden, drilling length, and charge, and prediction equations were derived. The characteristics of ground vibration, which was changed according to the priming location, was analyzed by using the nomogram of peak particle velocity (PPV) record. Attenuation relations, which were also dependent on the priming location, were analyzed. In this case, four different amounts of charge, that is, 0.5, 1.6, 5, and 15 kg, were used for the test. This criterion of charge amount is specified in the "Blasting design and construction guidelines to road construction" by the Ministry of Land, Transport and Maritime Affairs of Korea.

• Structural Engineering and Mechanics
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• v.49 no.1
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• pp.95-110
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• 2014

The study deals with physical modeling of space frame-pile foundation and soil system using finite element models. The superstructure frame is analyzed using complete three-dimensional finite element method where the component of the frame such as slab, beam and columns are descretized using 20 node isoparametric continuum elements. Initially, the frame is analyzed assuming the fixed column bases. Later the pile foundation is worked out separately wherein the simplified models of finite elements such as beam and plate element are used for pile and pile cap, respectively. The non-linear behaviour of soil mass is incorporated by idealizing the soil as non-linear springs using p-y curve along the lines similar to that by Georgiadis et al. (1992). For analysis of pile foundation, the non-linearity of soil via p-y curve approach is incorporated using the incremental approach. The interaction analysis is conducted for the parametric study. The non-linearity of soil is further incorporated using iterative approach, i.e., secant modulus approach, in the interaction analysis. The effect the various parameters of the pile foundation such as spacing in a group and configuration of the pile group is evaluated on the response of superstructure owing to non-linearity of the soil. The response included the displacement at the top of the frame and bending moment in columns. The non-linearity of soil increases the top displacement in the range of 7.8%-16.7%. However, its effect is found very marginal on the absolute maximum moment in columns. The hogging moment decreases by 0.005% while sagging moment increases by 0.02%.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.1
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• pp.55-77
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• 2012

A Modern Rock TBM is a tunnel excavation method combining the conventional tunnelling method with the mechanized tunnelling method. It is a hybrid system that excavates a tunnel with TBM and supports the ground by ring beam, wire mesh, rock bolt, shotcrete, i.e., conventional tunnelling method. In the Modern Rock TBM, a ring beam is similar to a steel rib in NATM in the way that uses H-beam. But using a ring beam is more effective than a steel rib because it is installed in a closed-circle. Therefore, improving the performance of the ring beam is a key factor for achieving tunnel stability. In this respect, this study introduces a pressurized ring beam that might be functioning more effectively by confining convergence during tunnel excavation. In order to verify the effect of the pressurized ring beam, a three-dimensional numerical analysis was conducted. The numerical analysis confirms an increase in the minimum principal stress and reduction in the plastic strain that triggers excessive displacement. The analysis result also indicates a decrease in the relative displacement occurring after installing the ring beam, and expansion in spacing between the ring beams.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.1
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• pp.102-109
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• 2016

The hydrodynamic interaction between two large vessels can't be neglected when two large vessels are closed to each other in restricted waterways such as in a harbor or narrow channel. This paper is mainly concerned with the ship maneuvering motion based on the hydrodynamic interaction effects between two large vessels moving each other in curved narrow channel. In this research, the characteristic features of the hydrodynamic interaction forces between two large vessels are described and illustrated, and the effects of velocity ratio and the spacing between two vessels are summarized and discussed. Also, the Inchon outer harbor area through the PALMI island channel in Korea was selected, and the ship maneuvering simulation was carried out to propose an appropriate safe speed and distance between two ships, which is required to avoid sea accident in confined waters. From the inspection of this investigation, it indicates the following result. Under the condition of $SP_{12}{\leq}0:5L$, it may encounter a dangerous tendency of grounding or collision due to the combined effect of the interaction between ships and external forces. Also considering the interaction and wind effect as a parameter, an overtaken and overtaking vessel in narrow channel can navigate while keeping its own original course under the following conditions; the lateral separation between two ships is about kept at 0.6 times of ship length and 15 degrees of range in maximum rudder angle. On the other hand, two ships while overtaking in curved narrow channel such as Inchon outer harbor in Korea should be navigated under the following conditions; $SP_{12}$ is about kept at 1.0 times of ship length and the wind velocity should not be stronger than 10 m/s.

• Journal of the Korean Vacuum Society
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• v.15 no.4
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• pp.360-366
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• 2006

We have performed density functional theory calculations for the surface structure of O/Pd(100)-p($2{\times}2$), formed by the adsorption of oxygen atoms of 0.25 ML. The oxygen atoms adsorb preferentially at the fourfold hollow site, and the calculated O-Pd bond length is $2,15{\AA}$, The first interlayer spacing ($d_{12}$) of Pd(100) expands by +0.8% due to the oxygen adsorption, which differs from the experimental value of +3.6% reported by a previous LEED study. Assuming that the LEED sample was possibly contaminated by hydrogen atoms, we also examined the effect of hydrogen impurities on the surface structure. Hydrogen atoms adsorbed on O/Pd(100)-p($2{\times}2$) are found to result in large expansions of $d_{12}$ of Pd(100). Our analysis estimates the amount of hydrogen atoms remaining on the LEED sample as -0.3 ML.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.2170-2174
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• 2005

Selective Laser Sintering (SLS) is a useful rapid prototyping technique for the manufacture of three dimensional (3D) solid objects directly from a scanning data. A new approach called a Selective Multi-Laser Sintering (SMLS) system has been developed at Korea Institute Machinery & Materials (KIMM) as an industrial type SFFS. This SMLS machine is built with a frame, heaters, nitrogen supply part, laser system. This system uses the dual laser and 3D scanner made in $Solutionix^{TM}$ to improve the precision and speed for large objects. The three-dimensional solid objects are made of polyamide powder. The investigation on each part of SMLS system is performed to determine the proper theirs design and the effect of experimental parameters on making the 3D objects. The temperature of the system has a great influence on sintering the polymer. Because the stability of the powder temperature prevents the deformation of each layer, the controls of the temperature in both the system and the powders are very important during the process. Therefore, we simulated the temperature distribution of build room using the temperature analysis with ANSYS program. Selected radiant heater is used to raise temperature of powder to melting point temperature. The laser parameters such as scan spacing, scan speed, laser power and laser delay time affect the production the 3D objects too. The combination of the slow scan speed and the high laser power shows the good results without the layer curling. The work is under way to evaluate the effect of experimental parameters on process and to produce the various objects. We are going to experiment continuously to improve the size accuracy and surface roughness.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1243-1251
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• 2020

Irradiation-induced damage of binderless nanoporous-isotropic graphite (NPIG) prepared by isostatic pressing of mesophase carbon microspheres for molten salt reactor was investigated by 3.0 MeV He⁺ irradiation at room temperature and high temperature of 600 ℃, and IG-110 was used as the comparation. SEM, TEM, X-ray diffraction and Raman spectrum are used to characterize the irradiation effect and the influence of temperature on graphite radiation damage. After irradiation at room temperature, the surface morphology is rougher, the increase of defect clusters makes atom flour bend, the layer spacing increases, and the catalytic graphitization phenomenon of NPIG is observed. However, the density of defects in high temperature environment decreases and other changes are not obvious. Mechanical properties also change due to changes in defects. In addition, SEM and Raman spectra of the cross section show that cracks appear in the depth range of the maximum irradiation dose, and the defect density increases with the increase of irradiation dose.

• International Journal of Fluid Machinery and Systems
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• v.5 no.2
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• pp.65-71
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• 2012

The objective of the present investigation is to explore the possibility of improving the performance of a centrifugal fan at low Reynolds numbers using a simple passive means, namely Gurney flap (GF). GFs of 1/$8^{th}$ inch brass angle (3.175 mm) corresponding to 15.9% of blade exit height or 5.1% of blade spacing at the impeller tip are attached to the impeller blade tip on the pressure surface. Performance tests are carried out on the centrifugal fan with vaneless diffuser at five Reynolds numbers (viz., 0.30, 0.41, 0.55, 0.69, $0.82{\times}10^5$, i.e., at five speeds respectively at 1,100, 1,500, 2,000, 2,500 and 3,000 rpm) without and with GF. Static pressures on the vaneless diffuser hub and shroud are also measured for each speed at four flow coefficients [${\phi}$=0.23 (below design flow coefficient), ${\phi}$=0.34 (design flow coefficient), ${\phi}$=0.45 (above design flow coefficient) and ${\phi}$=0.60 (above design flow coefficient)] with and without GF. From the performance curves it is found that the performance of the fan improves considerably with GFs at lower Reynolds numbers and improves marginally at higher Reynolds number. Similar improvements are observed for the static pressures on the diffuser hub and shroud. The effect of Reynolds number on the performance and static pressures is considerable. However the effect is reduced with GFs.

• Geomechanics and Engineering
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• v.19 no.6
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• pp.485-498
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• 2019

Pre-tensioned rock bolts can be classified into fully anchored, lengthening anchored and point anchored bolts based on the bond length of the resin or cement mortar inside the borehole. Bolts in varying anchoring methods may significantly affect the supporting effect of surrounding rock around a tunnel. However, thus far, the theoretical basis of selecting a proper anchoring method has not been thoroughly investigated. Based on this problem, 16 schemes were designed while incorporating the effects of anchoring length, pretension, bolt length, and spacing, and a systematic numerical experiment was performed in this paper. The distribution characteristics of the stress field in the surrounding rock, which corresponded to various anchoring scenarios, were obtained. Furthermore, an analytical approach for computing the active and passive strengthening index of the anchored surrounding rock is presented. A new fully anchoring method with pretension and matching technology are also provided. Then, an isolated loading model of the anchored surrounding rock was constructed. The physical simulation test for the bearing capacity of the model was performed with three schemes. Finally, the strengthening mechanism of varying anchoring methods was validated. The research findings in this paper may provide theoretical guidelines for the design and construction of bolting support in tunnels.