• Tunnel and Underground Space
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• v.10 no.1
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• pp.59-69
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• 2000

Acoustic emission is n burst of microseismic waves generated by microscopic failure due to deformation in materials. The study on the detection of initiation and propagation of microcracks from acoustic emission measurement is very important for the evaluation of the stability of underground rock structures by the nondestructive letting method. In this study, acoustic emission was measured under uniaxial stiffness loading test used to obtain the complete stress-strain curves of marble and concrete used as reinforced materials of rock structures. The analysis of acoustic emission parameters and source location were performed to discuss the characteristics of the deformation and failure behavior of rock and concrete. And acoustic emission was measured under cyclic loading test to verify the Kaiser effect associated with the damage of materials, in situ stress of rock, and stress history of concrete structure.

• Tunnel and Underground Space
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• v.15 no.1 s.54
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• pp.47-54
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• 2005

One of the standard procedures of discontinuity survey is the joint set identification from the population of field orientation data. Discontinuity set identification is fundamental to rock engineering tasks such as rock mass classification, discrete element analysis, key block analysis. and discrete fracture network modeling. Conventionally, manual method using contour plot had been widely used for this task, but this method has some short-comings such as yielding subjective identification results, manual operations, and so on. In this study, the method of discontinuity set identification using genetic algorithm was introduced, but slightly modified to handle the orientation data. Finally, based on the genetic algorithm, we developed a FORTRAN program, Genetic Algorithm based Clustering(GAC) and applied it to two different discontinuity data sets. Genetic Algorithm based Clustering(GAC) was proved to be a fast and efficient method for the discontinuity set identification task. In addition, fitness function based on variance showed more efficient performance in finding the optimal number of clusters when compared with Davis - Bouldin index.

• Tunnel and Underground Space
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• v.16 no.4 s.63
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• pp.334-346
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• 2006

The discrete element code in 2-D, PFC2D, has been used as a tool to simulate various phenomena in rock mechanics and rock engineering. However, the code has an disadvantage that procedure to determine micro-parameters, namely properties of particles and contacts is repetitive and time-consuming. In this study, we analyzed the effect of micro-parameters(for generation of a contact-bonded model) on macro-properties(that were measured numerically by uniaxial compressive test). Based on the analysis, also, the time-saving and reliable method was suggested to determine a complete set of micro-parameters. In order to verify the suggested method, numerical specimens were generated in PFC2D for 10 different rock types at home and abroad. By the two trials for each specimen, in the result, the Young's modulus, Poisson's ratio and uniaxial compressive strength could be reproduced with being in relative error by about 5% to the values obtained by laboratory tests.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.283-292
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• 2016

A computer program code was developed to estimate hydraulic behavior of the 2-D connected pipe network system, and implemented to evaluate the effect of joint aperture on hydraulic parameters of fractured rock masses through numerical experiments. A total of 216 stochastic 2-D DFN(discrete fracture network) blocks of $20m{\times}20m$ were prepared using two joint sets with fixed input parameters of joint orientation, frequency and size distribution. Two different cases of joint aperture variation are considered in this study. The hydraulic parameters were estimated for generated 2-D DFN blocks. The hydraulic anisotropy and the chance for equivalent continuum behavior of the DFN system were found to depend on the variability of joint aperture.

• Tunnel and Underground Space
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• v.18 no.1
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• pp.1-9
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• 2008

Acoustic emission (AE) and Microseimsic (MS) activities are law-energy seismic events associated with a sudden inelastic deformation such as the sudden movement of existing fractures, the generation of new fractures or the propagation of fractures. These events rapidly increase before major failure and happen within a given rock volume and radiate detectable seismic waves. The main difference between AE and MS signals is that the seismic motion frequencies of AE signals are higher than those of MS signals. As the failure of geotechnical structures usually happens as a high velocity and small displacement, it is nat easy ta determine the precursor and initiation stress level of failure in displacement detection method. To overcame this problem, AE/MS techniques far detection of structure failure and damage have recently adapt in civil engineering. This study deal with the basic theory of AE/MS and state of arts in monitoring technique using AE/MS.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.37-41
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• 2018

As individuals generate and share various content anytime and anywhere, new networking architectures, such as content-centric networking (CCN) using the content name as a packet identifier, have been in the spotlight recently. However, the current CCN hardly takes into account node mobility problems, especially the mobility of content sources. The movement of content sources causes long delivery latency and long service disruptions. To solve that, the tunneling-based redirection scheme was proposed. However, the tunneling-based scheme requires a location-update procedure whenever the network changes, which creates many control messages and causes long latency. So, this paper presents hierarchical mobility management of mobile CCN to reduce the number of control messages and handoff latency. Performance evaluation shows that the proposed scheme can provide low control overhead, which results in network scalability.

• Tunnel and Underground Space
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• v.9 no.2
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• pp.131-140
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• 1999

Although there have been lots of geological or geotechnical surveys for construction sites, most of data obtained from these surveys have not been reused properly for the future construction work due to the absence of systematic management of data management system. This research, therefore, has focused on the development of DB system, Rockmass Information Management System(RIMS), to save, manage and reuse these abandoned data, specially test data of rock and rockmass with site conditions. RIMS has not only the basic functions of inputting, modifying, and dynamic searching of data but also several data control modules which can manage, input and correct, analyse and report data. Furthermore it saves data such as strata status, laboratory test results, in-site test results, and so on using 3-dimensional data stacking up structure. It is using x, y coordinates to represent horizontal positions and depth to represent vertical position of data. With the development of RIMS, this research has analyzed and classified present conditions of data in RIMS according to region, rock type, etc.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.8
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• pp.674-680
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• 2014

In this paper, as one of the fusion of IT and ocean technology, we propose a scheme to support NEMO in a harbor area network to provide network mobility for passengers, distribution as well as give a connection to an MN from an outside network. In a harbor area under PMIPv6 with NEMO support, a problem could be occurred due to overlapping HA/LMA tunnels and duplicate BCE fields. To Solve these problems, we consider the existing mobility option and add an optional field in the PBU message, which can notify the LMA and HA for either an initial connection or handover request. This procedure can reduce some overlapped steps of binding procedure. Hence, our proposed scheme could reduce an amount of delay and save the processing resource in the harbor area under PMIPv6 with NEMO support.

• Applied Chemistry for Engineering
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• v.24 no.5
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• pp.562-565
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• 2013

The high purity Al foil, which has an enlarged surface area by electrochemical etching process, has been used as an anode for an aluminum electrolytic capacitor. Etch pits are randomly distributed on the surface because of the existence of surface irregularities such as impurity and random nucleation of pits. Even though a large surface area was formed on the tunnel-etched Al, its applications to various fields were limited due to non-uniform tunnel morphologies. In this work, the selective electrochemical etching of aluminum was carried out by using a patterned mask fabricated by photolithographic method. The formation of etch pits with uniform distribution has been demonstrated by the optimization of experimental conditions such as current density and etching solution temperature.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.12
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• pp.9-16
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• 2011

Most of the current mobility management protocols such as MIPv4/6 and its variants standardized by the IETF do not support global seamless handover. This is because they require comprehensive changes of the existing network infrastructure. In this article, we propose a simple mobility management protocol (SMMP) which can support global seamless handover between homogeneous or heterogeneous wireless networks. The idea is that the SMMP employs separate location management function as done in SIP to support global user and service mobility. In addition, the bidirectional tunnels are dynamically constructed to support seamless IP mobility by extending the IEEE 802.21 MIH standards. The detailed architecture and functions of the SMMP have been designed. Finally, the simulation results, using NS-2, show that the proposed SMMP outperforms the existing MIPv6 and HMIPv6 in terms of handover latency, packet loss, pear signal noise ratio (PSNR).