• International journal of advanced smart convergence
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• v.2 no.1
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• pp.36-41
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• 2013

Decision-making is to extract information that can be executed in the future, it refers to the process of discovering a new data model that is induced in the data. In other words, it is to find out the information to peel off to find the vein to catch the relationship between the hidden patterns in data. The information found here, is a process of finding the relationship between the useful patterns by applying modeling techniques and sophisticated statistical analysis of the data. It is called data mining which is a key technology for marketing database. Therefore, research for cluster analysis of the current is performed actively, which is capable of extracting information on the basis of the large data set without a clear criterion. The EM and K-means methods are used a lot in particular, how the result values of evaluating are come out in experiments, which are depending on the size of the data by the type of distance-based and probability-based data analysis.

• Journal of Ocean Engineering and Technology
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• v.31 no.2
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• pp.170-176
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• 2017

In this paper, we propose an underwater localization scheme through the fusion of an inertial navigation system (INS) and the received signal strength (RSS) of electromagnetic (EM) wave sensors to guarantee precise localization performance with high sampling rates. In this localization scheme, the INS predicts the pose of the unmanned underwater vehicle (UUV) by dead reckoning at every step, and the RF sensors corrects the UUV position functions using the Earth-fixed reference when the UUV is located in underwater wireless sensor networks (UWSN). The localization scheme and state modeling were conducted in the extended Kalman filter framework, and UUV localization experiments were conducted in a basin environment. The scheme achieved reliable localization accuracy during long-term navigation, demonstrating the feasibility of exploiting EM wave attenuation as Earth-fixed reference sensors.

• Journal of the Korean Geophysical Society
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• v.9 no.3
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• pp.159-169
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• 2006

A GDS (Geomagnetic Depth Sounding) method, one of extremely low-frequency EM methods, has been carried out to examine conductivity anomalies in and around the Korean Peninsula. In this study, new GDS data acquired at the five sites in south-eastern area of the peninsula were incorporated into the previous GDS data. In order to quantitatively interpret observed induction arrows, the 3-D MT modeling considering the surrounding seas of the Korean Peninsula has been performed to evaluate sea effect at each GDS site. The modeling results revealed that the observed real induction arrows were not explained by solely sea effects, consequently two conductive structures that are responsible for the discrepancies between observed and calculated induction arrows were proposed. The first one is the Imjingang Belt, which is thought as an extension of Quiling-Dabie-sulu continental collision belt. The effects of the Imjingang Belt clearly appear at the site YIN and ICHN. The second one is the HCL (Highly Conductive Layer), which is considered as a conductive anomaly by mantle upwelling produced in back-basin region. The effects of the HCL are seen at the site KZU, KMT101, and KMT 107 in the south-eastern region of the Korean Peninsula.

• Geophysics and Geophysical Exploration
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• v.14 no.2
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• pp.164-175
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• 2011

Using natural electromagnetic (EM) fields at low frequencies, magnetotelluric (MT) surveys can investigate conductivity structures of the deep subsurface and thus are used to explore geothermal energy resources and investigate proper sites for not only geological $CO_2$ sequestration but also enhanced geothermal system (EGS). Moreover, marine MT data can be used for better interpretation of marine controlled-source EM data. In the interpretation of MT data, MT modeling schemes are important. This study improves a three dimensional (3D) MT modeling algorithm which uses edge finite elements. The algorithm computes magnetic fields by solving an integral form of Faraday's law of induction based on a finite difference (FD) strategy. However, the FD strategy limits the algorithm in computing vertical magnetic fields for a topographic model. The improved algorithm solves the differential form of Faraday's law of induction by making derivatives of electric fields, which are represented as a sum of basis functions multiplied by corresponding weightings. In numerical tests, vertical magnetic fields for topographic models using the improved algorithm overcome the limitation of the old algorithm. This study recomputes induction vectors and tippers for a 3D hill and valley model which were used for computation of the responses using the old algorithm.

• Geophysics and Geophysical Exploration
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• v.1 no.2
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• pp.127-135
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• 1998

The Born approximation is widely used for solving the complex scattering problems in electromagnetics. Approximating total internal electric field by the background field is reasonable for small material contrasts as long as scatterer is not too large and the frequency is not too high. However in many geophysical applications, moderate and high conductivity contrasts cause both real and imaginary part of internal electric field to differ greatly from background. In the extended Born approximation, which can improve the accuracy of Born approximation dramatically, the total electric field in the integral over the scattering volume is approximated by the background electric field projected to a depolarization tensor. The finite difference and elements methods are usually used in EM scattering problems with a 2D model and a 3D source, due to their capability for simulating complex subsurface conductivity distributions. The price paid for a 3D source is that many wavenumber domain solutions and their inverse Fourier transform must be computed. In these differential equation methods, all the area including homogeneous region should be discretized, which increases the number of nodes and matrix size. Therefore, the differential equation methods need a lot of computing time and large memory. In this study, EM modeling program for a 2D model and a 3D source is developed, which is based on the extended Born approximation. The solution is very fast and stable. Using the program, crosshole EM responses with a vertical magnetic dipole source are obtained and the results are compared with those of 3D integral equation solutions. The agreement between the integral equation solution and extended Born approximation is remarkable within the entire frequency range, but degrades with the increase of conductivity contrast between anomalous body and background medium. The extended Born approximation is accurate in the case conductivity contrast is lower than 1:10. Therefore, the location and conductivity of the anomalous body can be estimated effectively by the extended Born approximation although the quantitative estimate of conductivity is difficult for the case conductivity contrast is too high.

• Geophysics and Geophysical Exploration
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• v.5 no.2
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• pp.84-92
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• 2002

In this study, the new modeling scheme has been developed for recently designed and tested electromagnetic survey, which adapts horizontal magnetic dipole with $1\;kHz\~1\;MHz$ frequency range as a source. The 2.5-D secondary field formulation in wavenumber domain was constructed using finite element method and verified through comparing results with layered-earth solutions calculated by integral equations. 2-D conductive- and resistive-block models were constructed for calculating electric field, magnetic field and impedance - the ratio of electric and magnetic fields which are orthogonal each other. This study showed that electric field and impedance are superior in identifying 2-D isolated-body model to magnetic field. In particular, impedance gives more stable results than electric field with similar spatial resolving power, because electric field is divided by magnetic field in impedance. Thus the impedance analysis which uses electric and magnetic fields together would give better result in imaging the shallow anomalies than conventional EM method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.2
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• pp.167-175
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• 2011

The purpose of this study is to examine the impact that change in speed and modeling methods has on maglevs' runnability. The study constructed equations of motion on 4-DOF, 6DOF, and 10-DOF vehicles respectively and carried out numerical analysis, applying 4th Runge Kutta method, in order to run six different model maglev as changing the vehicles speed on the same bridge that had 2000 to 1 deflection. The analysis revealed that maglev's runnability improved as speed was lower and the specific model had higher number of bogey and EMS.

• Speech Sciences
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• v.14 no.1
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• pp.163-174
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• 2007

All observation has uncertainty due to noise or channel characteristics. This uncertainty should be counted in the modeling of observation. In this paper we propose a modified optimization object function of a GMM training considering inexact observation. The object function is modified by introducing the concept of observation confidence as a weighting factor of probabilities. The optimization of the proposed criterion is solved using a common EM algorithm. To verify the proposed method we apply it to the speaker recognition domain. The experimental results of text-independent speaker identification with VidTimit DB show that the error rate is reduced from 14.8% to 11.7% by the modified GMM training.

• Proceedings of the Acoustical Society of Korea Conference
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• 1998.06c
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• pp.171-174
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• 1998

본 논문에서는 음성합성(speech synthesis) 및 부호화(coding) 시스템에 있어서 음원(voice source) 모델링에 관한 문제를 살펴보고자 한다. 기존의 음원 모델링 시스템이 가지고 있는 여러 문제들을 극복하고자 기저함수(basis function) 의 가중 합(weighted-sum)으로 음원을 모델링 하는 새로운 기법을 제안하고자 한다. 제안한 방법에서는 음원 파형(voice source waveform)을 적절히 표현하기 위해서 필터뱅크(filter bank)에 기초한 기저함수의 가중 합으로 나타낸다. 다양한 음원 특성을 효과적으로 나타내는 음원 파라미터를 구하기 위하여 EM(estimate maximize)에 기초한 구조에 관해 조사한다. 제안한 방법을 이용하여 다양한 유성음에 대해 실험을 수행하였다. 실험결과 제안한 추정(estimation) 방법 및 모델링 방법을 이용하면 기존의 방법에 비해 더 정확한 음원 파형을 추정할 수 있고, 다양한 음원 특성을 나타낼 수 있다. 또한 음성합성 및 부호화에서도 음성품질(voice quality)를 개선시킬 수 있으리라 기대된다.

• Journal of the Korean Applied Science and Technology
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• v.27 no.1
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• pp.61-69
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• 2010

This study is focused on the modeling of two phase fluid flow system in the electrode of hydrogen gas generator. The characteristics of hydrogen gas generation was studied in view of efficiency of hydrogen gas generation rate and a tendency of gas flow through the riv of electrode. Since the flow rate of generated gas is the most crucial in determining the efficiency of hydrogen gas generator, we adopted the commercial analytical program of COMSOL $Multiphysics^{TM}$ to calculate the theoretical flow rate of hydrogen gas from the outlet of gas generator.