• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.28 no.2
• /
• pp.123-130
• /
• 2015

This paper presents a new formulation for transient simulations of microwave propagation in heterogeneous unbounded domains. In particular, perfectly-matched-layers(PMLs) are introduced to allow for wave absorption at artificial boundaries used to truncate the infinite extent of the physical domains. The development of the electromagnetic PML targets the application to engineering mechanics problems such as structural health monitoring and inverse medium problems. To formulate the PML for plane electromagnetic waves, a complex coordinate transformation is introduced to Maxwell's equations in the frequency-domain. Then the PML-endowed partial differential equations(PDEs) for transient electromagnetic waves are recovered by the application of the inverse Fourier transform to the frequency-domain equations. A mixed finite element method is employed to solve the time-domain PDEs for electric and magnetic fields in the PML-truncated domain. Numerical results are presented for plane microwaves propagating through concrete structures, and the accuracy of solutions is investigated by a series of error analyses.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.17 no.1
• /
• pp.75-82
• /
• 2004

With an aim at eliminating the numerical dispersion error arising from the numerical simulation of stress wave propagation, numerical dispersion characteristics of the wave equation based one-dimensional finite element model are analyzed and some dispersion control scheme are proposed in this paper The dispersion analyses are carried out for two types of mass matrix, namely the consistent and the lumped mass matrices. Based on the finding of the analyses, dispersion correction techniques are developed for both the implicit and explicit schemes. For the implicit scheme, either the weighting factor for the spatial derivatives of each time level or the lumping coefficient for mass matrix is adjusted to minimize the numerical dispersion. In the case of the explicit scheme an artificial dispersion term is introduced in the governing equation. The validity of the dispersion correction techniques proposed in this study is demonstrated by comparing the numerical solutions obtained using the Present techniques with the analytical ones.

• The KIPS Transactions:PartB
• /
• v.13B no.1 s.104
• /
• pp.15-20
• /
• 2006

This paper describes research on intelligent game character through performance enhancements of physics engine in computer games. The algorithm that recognizes the physics situation uses momentum back-propagation neural networks. Also, we present an experiment and its results, integration methods that display optimum performance based on the physics situation. In this experiment on integration methods, the Euler method was shown to produce the best results in terms of fps in a simulation environment with collision detection. Simulation with collision detection was shown similar fps for all three methods and the Runge-kutta method was shown the greatest accuracy. In the experiment on physics situation recognition, a physics situation recognition algorithm where the number of input layers (number of physical parameters) and output layers (destruction value for the master car) is fixed has shown the best performance when the number of hidden layers is 3 and the learning count number is 30,000. Since we tested with rigid bodies only, we are currently studying efficient physics situation recognition for soft body objects.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.8 no.2
• /
• pp.9-20
• /
• 1998

In this paper, a new distance relaying scheme is proposed. Artificial neural networks are applied to the distance relaying system composed of pattern recognition based. The proposed distance relaying scheme has two blocks of pattern recognition stages to estimate the fundamental frequency and to classify the fault types. In the first block, a filtering method using neural networks called a neural networks mapping filter(NMF) is presented to efficiently extract the features. And in the sec'ond block, the estimator called neural networks fault pattern estimator(NFPE) is also presented to classify the fault types by the extracted effective features obtained from NMF. Each block of these applied schemes is trained by back-propagation algorithm of multilayer perceptron and show the fast and accurate pattern recognition by ability of multilayer neural networks. The test result of this approach are obtained the good performance from the fault transient wave signals of EMTP(e1ectromagnetic transients program) in the various fault conditions of power systems.

• Journal of Ocean Engineering and Technology
• /
• v.4 no.2
• /
• pp.250-250
• /
• 1990

In this paper, fatigue tests were carried out at stress test levels of 461 MPa, 441 MPa, and 431 MPa by using smooth specimen of$2_{1/4}$ Cr-1 Mo steel with the stress ratio(R) of 0.05. The initiation, growth and coalescense process of the major cracks and sub-cracks among the fatigue cracks on the smooth specimen are investigated and measured under each stress level at a constant cycle ratio by the replica technique with optical microscope. Some of the important results are as follows: In spite of the difference of stress levels, the major crack data gather into a small band in the curve of surface crack length and crack depth against cycle ratio N/Nf. The sub-crack data, however, deviate from the band of the major crack. The growth rates, da/dN, of major and sub-crack plotted against the stress intensity factor range, ${\Delta}K$, have the tendency to be compressed on a relatively small band. But it is more effective to predict fatigue life through major cracks. The propagation behavior of surface microcracks on the smooth specimens coincides with that of the specimen having an artificial small surface defect or through crack.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.31 no.3 s.258
• /
• pp.344-354
• /
• 2007

The objective of this study is to investigate the effect of arbitrarily located defect around the circular hole in the aircraft structural material such as Al/GFRP laminates and monolithic Al alloy sheet under cyclic bending moment. The fatigue behavior of these materials may be different due to the defect location. Material flaws in the from of pre-existing defects can severely affect the fatigue crack initiation and propagation behavior. The aim of this study is to evaluate effects of relative location of defects around the circular hole in monolithic Al alloy and Al/GFRP laminates under cyclic bending moment. The fatigue behavior i.e., the stress concentration factor($K_t$), the crack initiation life($N_i$), the relationship between crack length(a) and cycles(N), the relationship between crack growth rate(da/dN) and stress intensity factor range(${\Dalta}K$) near a circular hole are considered. Especially, the defects location at ${\theta}_1=0^{\circ}\;and\;{\theta}_2=30^{\circ}$ was strongly effective in stress concentration factor($K_t$) and crack initiation life($N_i$). The test results indicated the features of different fatigue crack propagation behavior and the different growing delamination shape according to each location of defect around the circular hole in Al/GFRP laminates.

• The Journal of the Korea Contents Association
• /
• v.7 no.12
• /
• pp.292-302
• /
• 2007

Thousands of studies on predicting information and products that are suitable for customers' preference have been actively proceeding. In massive information, unnecessary information should be removed to satisfy customers' needs. This Information filtering has been proceeding with several methods such as content-based and collaborative filtering etc. These conventional filtering methods have scarcity and scalability problems. Thus, this paper proposes a recommendation system using BPN to solve them. Data obtained by survey questionnaire are used as training data of neural network. The recommendation system using neural network is expected to recommend suitable products because it creates optimal network. Finally, the prototype for recommendation system based on neural network is proposed to collect data and recommend appropriate methods through survey questionnaire. As a result, this research improved the problems of conventional information filtering.

• Korean Journal of Plant Tissue Culture
• /
• v.26 no.4
• /
• pp.271-274
• /
• 1999

This study was undertaken to develop an efficient propagation technique for mature Betula davurica. Using aseptic materials taken from in vitro culture, the effects of media and plant growth regulators on shoot proliferation and rooting were investigated. DKW medium turned out to be the best in shoot proliferation among the media tested. Whereas axillary buds were better culture material than apical buds in proliferation of shoots, apical buds were slightly better than axillary buds on shoot elongation. Neither 1 /2 MS nor WPM medium seemed to be suitable for shoot multiplication or elongation. When the explants were cultured on 1/2 MS medium, shoot elongation was retarded by forming big callus at the base. In the case of WPM, shoots could be formed normally, but they exhibited slow growing. NAA was so effective on in vitro rooting that more than 80% rooting could be achieved on half-strength DKW medium supplemented with 1.0 mg/L NAA after 4 weeks in cultures. Ex vitro rooting using elongated shoot was also applicable to rooting and acclimatization. Rooted plantlets were successfully acclimatized in an artificial soil mixture and grew normally. The results demonstrate that efficient mass propagation of mature B. davurica can be done through tissue culture.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.1 no.1
• /
• pp.9-18
• /
• 1968

A series of experiments since 1963 ha sbeen made on the artificial propagation of Penaeus oriental is for the purpose of improving breeding of the prawn. The results are as follows: 1. Spawning takes place in the evening, and almost completes before 10 o'clock p. m.. Number of spawns deposited by a prawn is 30,000 to 150,000. 2. Deposited spawns become nauplius stage after approximately 18 hours (about 13 hours in hatching tanks) at water temperature of $23\~25^{\circ}C$, and grow to first nauplius stage in subsequent 28 hours. 3. It takes about five days from first nauplius stage to zoea stage, and additional four or five days from first zoea stage to first mysis stage. 4. It takes approximately 2 to 3 weeks from spawning to post larva. 5. Hatching rate ranged from $1.4\%$ to $14.9\%$, with the average of $6\%$ in 1966 and $10\%$ to $35\%$ averaging $20\%$ in 1967.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.23 no.1
• /
• pp.15-36
• /
• 2020

The purpose of this study is to provide basic data for the establishment of the management plan of Seoullo 7017 after analyzing the characteristics of immigration plants in addition to those introduced plants. The taxa number of plants appeared as 276 taxa including 82 families, 161 genera, 246 species, 1 subspecies, 22 varieties and 7 forms. Among them, immigration plants appeared 79 classification groups, including 32 families, 65 genera, 77 species and 2 varieties. Invasive alien plants appeared as 22 classification groups in 79 classification groups of immigration plants. The ratio of America origin plants, second period(1932~1960) in introduction time and the wide diffusion species is high. In June, the growth and occurrence time of the immigration plants was the highest by monthly the characteristics of the growth of the immigration plants, the immigration plants appeared mostly. In case of dormancy form among life-form, the therophytes(th), in the propagation form-radicoid form, the R₅(monophyte), in the propagation form-disseminule form, the gravity D₄(having no special modification for dissemination), and in the growth form, the erect form(e) was high. The various immigration plants appeared in green areas covered by Zoysia japonica and low Hedera helix densities. This study is the first flora study since Seoullo 7017 was opened in 2017. And so continuous flora monitoring is required for Seoullo 7017.