• Proceedings of the KIEE Conference
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• 2007.04b
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• pp.55-57
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• 2007

오일 변압기 내부의 절연물은 절연지, 프레스보드, 광유 또는 식물유가 주로 사용되고 있다. 사용 기간과 과부하 조건에 따라 열화정도가 달라질 수 있으며, 내부 절연물의 열분해 및 가수분해로 인해 수분은 자연스럽게 생성될 수 있다. 생성된 수분은 절연을 약하게 하는 주된 요인으로 작용해 기기의 고장 또는 정전을 초래할 수도 있다. 본 논문에서는 변압기 내부 절연물의 주파수응답 특성과 절연상태 값을 바탕으로 변압기 내부를 전기적 소자로 등가화하였다. 그 후 등가화된 회로를 이용해 회복전압법의 원리에 따라 EMTP 프로그램을 활용해 분극특성을 모의하였다. 실제 측정 값과의 비교를 위해 보고된 문헌의 데이터를 활용하였고, RVM을 이용한 실측값과 유사한 결과를 얻게 되었다. 따라서 본 시뮬레이션에 활용된 전기적 소자값을 변경함으로서 내부 절연물의 열화정도에 대한 기대 파형을 예측할 수 있는 유용한 도구로 활용될 수 있음을 확인하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2019.05a
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• pp.86-88
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• 2019

In a complex geographical environment, communication quality of communication equipment is being seriously challenged. Secondary Users(SUs) must make the best possible use the idle spectrums that Primary Users(PUs) do not use and change spectrum frequently. Using the relevance vector machine(RVM) to establish a signal noise Ratio(SNR) Model for interference information and bit error rate(BER). Through the model and real-time interference information, the minimum channel SNR meeting the BER requirements of communication equipment can be predicted, and we can also calculate the minimum transmitted power. According to the simulation results, this method has better performance for selecting available channel and restraining interference.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1996.04a
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• pp.662-666
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• 1996

The variations of the surface topographical parameters for the analysis of the pedestrian slip and fall accidents during the sliding friction between the specially prepared floor specimens and three working shoes were investigated. The profile ordinate data for each flooring specimen were obtained at 1.1 .mu.m intervals using a laser scanning confocal microscope system along to the direction of sliding. A number of surface roughness parameters, that is, the centre line average (c.l.a.) and root mean square (r.m.s.) roughness, maximum height (Rtm), maximum mean peak height (Rpm), maximum mean depth (Rvm), and average asperity slope were calculated using a computer program and compared with the dynamic friction results. The analysis showed that the surface parameters undergo marked variations during the sliding process, but the variations were statistically significant. It was found that amongst various surface parameters, the maximum depth (Rvm) and the average asperity slope of the asperities were the biggest variation during the sliding proceeding. This result confirms the previous study and may suggests a new approach to monitoring the flooring environments with their service as the effort to reduce the pedestrain slip accident.

• Transactions on Electrical and Electronic Materials
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• v.7 no.5
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• pp.230-234
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• 2006

One of the methods currently being investigated as a possible non-intrusive diagnostic tool for condition monitoring of power transformer and cable is the recovery voltage measurement, which will be improving the ability to detect the content of water concentration and the ageing process in the insulation system and may thus be an indicator of insulation quality and its ageing status. The polarization phenomenon was studied using RVM with oil-paper samples. In order to interpret its mechanism, the Extended Debye model was introduced. With different circuit parameters, various simulation results were gotten. Furthermore, with the test samples of different ageing condition, measurements are accomplished in the lab. On the basis of this experiment as well as theoretical analysis, correlations between polarizations and ageing were analyzed.

• Journal of Computing Science and Engineering
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• v.6 no.2
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• pp.105-118
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• 2012

We propose two new approaches that automatically parallelize Java programs at runtime. These approaches, which rely on run-time trace information collected during program execution, dynamically recompile Java byte code that can be executed in parallel. One approach utilizes trace information to improve traditional loop parallelization, and the other parallelizes traces instead of loop iterations. We also describe a cost/benefit model that makes intelligent parallelization decisions, as well as a parallel execution environment to execute parallelized programs. These techniques are based on Jikes RVM. Our approach is evaluated by parallelizing sequential Java programs, and its performance is compared to that of the manually parallelized code. According to the experimental results, our approach has low overheads and achieves competitive speedups compared to the manually parallelizing code. Moreover, trace parallelization can exploit parallelism beyond loop iterations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.3
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• pp.350-357
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• 1997

The transient incompressible flow behind the axisymmetric bluff body is numerically simulated using the random vortex method(RVM). Based on the vorticity formulation of the unsteady Navier-Stokes equations, the Lagrangian approach with a stochastic simulation of diffusion using random walk technique is employed to account for the transport processes of the vortex elements. The numerical solutions for 2-dimensional recirculating flow behind a backward-facing step in the laminar range of Reynolds number are compared with experimental data. The present simulation focuses on the transitional flow regime where the recirculation zone behind the bluff body becomes highly unsteady and large-scale vortex eddies are shed from the bluff body wake due to intrinsic shear layer instabilities. The unsteady vertical flow structures and the mixing characteristics behind the bluff body are discussed in detail.

• Ocean Systems Engineering
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• v.5 no.1
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• pp.41-54
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• 2015

This study presents the development of predictive models for uplift capacity of suction caisson in clay using an artificial intelligence technique, extreme learning machine (ELM). Other artificial intelligence models like artificial neural network (ANN), support vector machine (SVM), relevance vector machine (RVM) models are also developed to compare the ELM model with above models and available numerical models in terms of different statistical criteria. A ranking system is presented to evaluate present models in identifying the 'best' model. Sensitivity analyses are made to identify important inputs contributing to the developed models.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1999-2004
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• 2004

Experiments were conducted to investigate the flow characteristics of water through rectangular PDMS microchannels with a hydraulic diameter ranging from 66.67 to 200 ${\mu}m$. In the experiments, the flow rate and pressure drop across the microchannels were measured at steady states. The experimental results were compared with the predictions from the conventional laminar flow theory. A significant difference between the experimental data and the theoretical predictions was found. Experimental results indicate that the pressure gradient and flow friction in microchannels are higher than those from the conventional laminar flow theory. This may be attributed to the fact that there exists effect of surface roughness of the microchannels. In this study, a surface roughness model is implemented to interpret the experimental data. A good agreement between the experimental data and the numerical predictions with a surface roughness model were found.

• Wind and Structures
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• v.9 no.1
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• pp.59-74
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• 2006

Vertical stabilizer plates have been found to be an effective aerodynamic measure to improve the aerodynamic stability of bridges either with an open cross section or with a streamlined box cross section in wind tunnel testings and have been adopted in some long span bridges. By taking an open deck II-shaped section and a closed box section as examples, the mechanism of vertical stabilizer plates for improving aerodynamic stability are investigated by using numerical simulation based on Random Vortex Method. It is found that vertical stabilizer plates can increase the amplitude of the heaving motion, and decrease that of the rotational motion of the bridge decks.

• Computers and Concrete
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• v.24 no.1
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• pp.7-17
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• 2019

The complex phenomenon of the bond formation in geopolymer is not well understood and therefore, difficult to model. This paper present applied statistical models for evaluating the compressive strength of geopolymer. The applied statistical models studied are divided into three different categories - linear regression [least absolute shrinkage and selection operator (LASSO) and elastic net], tree regression [decision and bagging tree] and kernel methods (support vector regression (SVR), kernel ridge regression (KRR), Gaussian process regression (GPR), relevance vector machine (RVM)]. The performance of the methods is compared in terms of error indices, computational effort, convergence and residuals. Based on the present study, kernel based methods (GPR and KRR) are recommended for evaluating compressive strength of Geopolymer concrete.