• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.3
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• pp.419-428
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• 2000

Multiconductor transmission line(MTL) equations are solved by FDTD(Finite-Difference Time-Domain) method to predict crosstalk and fields to transmission line coupling on lossy multiconductor transmission lines terminated in arbitrary linear loads. Skin effect losses as well as dc losses are included in the analysis. In order to increase computational efficiency, the convolution integral of internal impedance of conductors and the line currents is computed by using Prony method. For boundary conditions of MTLs terminated in linear loads, state-variable formulation is adopted. The simulated results by FDTD method are compared with the measured ones obtained by using TEM cell. The predictions are in good agreement with the measurements. In addition, it has been found that skin effect losses as well as dc losses of the conductors should be included for accurate predictions on relatively high loss transmission lines such as PCB. It has also been found that dc losses and skin-effect losses affect late-time responses and early-time responses, respectively.

• Geotechnical Engineering
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• v.14 no.5
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• pp.191-204
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• 1998

The feasibility of fly ash was evaluated as an alternative liner material to the conventional clay liner of landfills through modeling and laboratory experiments. In order to consider the effect of unsaturation on water flow through the liner, analyses were made to compare flow characteristics in saturated liner with that of unsaturated one. Contaminant migration characteristics in liners were investigated by batch experiment and modeling, in which phenol was employed as a model was solved by numerical techniques of finite difference method and predictor-corrector method to deal with high non-linearity. Sequential method was used to handle the system of differential equations. Results show that the alternative liner material is more capable of cutting off water flow in unsaturated condition and in preventing phenol from passing through it. It can be seen that, under the flow conditions considered in this study, the conventional saturation approach underestimates the amount of water passing through the liner and doers the cut-off capability against phenol significantly.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.9 no.4
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• pp.251-255
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• 1976

Three hundred and sixty two specimens of Plecoglossus altivelis were randomly sampled from Chunji Stream in Seogwipo, Cheju-Do, during the period from 25 Aug., 1973 to 14 Feb., 1974 to investigate the relationship between total length and dody weight as well as the condition factor during the spawning period. Results obtained are summarized as follows : The relationships between total length and body weight are calculated as below, respectively : $W=0.008639\;L^{3.1806}$ : Prior to spawning period $W=0.01830\;L^{2.7689}$ : During spawning period The above equations differ each other significantly. Nevertheless, the significant difference is not found between sexes. The mean body length decreased during the spawning season. The fact seems to be caused by the death of large fish after spawning. The condition factor was $13.45\%_{\circ}$ on the average in August. The value decreased continuously from September, giving the minimum mean value of $10.25\%_{\circ}$ on Nobember 29. But the value increased again, showing $11.18\%_{\circ}$ in next February. Majority of the fish survived until next year was small ranging from 11 to 12cm in total length.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.6
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• pp.511-519
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• 1992

A microcomputer based control system was constructed to save energy consumption in the thermal sterilizing process. The functional accuracy of system was evaluated through the analysis of the thermal diffusivities of the model solid food, Alaska pollack surimi. The heat penetration curves obtained through the experiments were typical for solid foods. The practical thermal diffusivity calculated from heat penetration curve was a constant value at steady sterilizing temperature, and this was independent of the holding time. At different temperatures, the thermal diffusivity values did not show remarkable differences when compared with those predicted by some experimental equations cited from the literatures. The maximal difference was within the range of $\pm10.0\%$.

• Journal of the Korean School Mathematics Society
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• v.3 no.2
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• pp.69-82
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• 2000

Mathematics is the subject that requires high mental function such as the ability of logically thinking and investigating. Because of the reason there exists much greater difference in students' individual scholastic abilities in mathematics class than in other classes. Recently many schools organize students into two or three level-based mathematics classes according to each student's level to solve the problem. But in spite of its many merits the new system of class organization has some problems. The problem which is pointed out as the most serious thing frequently is that many teachers still use the same textbook and the same teaching method for all students, not considering student's level. Obviously it causes the reduction of students' interest and motivation. In this point of view, I tried to solve such a problem by development and application of level learning materials reconstructed text book according to students' abilities and levels through this research. As the result of the research to examine the changes of students' emotional factors such as the recognition, interest, and attitude which influence on improving self-educability in learning mathematics has occurred, the following conclusion comes out. 1. Through the mathematics class utilizing level learning materials reconstructed textbook, students come to recognize that level learning materials are more effective than uniformed contents of the same textbook and get more active learning attitude. 2 The application of level learning materials in a level-based class has contributed to increasing students' interest in mathematics. Furthermore it was also effective in the positive changes of students' emotional factors such as the recognition, interest, and attitude which influence on improving self-educability in learning mathematics.

• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.439-448
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• 2001

A two-dimensional finite difference numerical model was developed in order to simulate two-phase fluid flow in a single fracture. In the model, variation of viscosity with pressure and that of relative permeability with water saturation can be treated. For the numerical solution, IMPES method was used, from which the pressure and the saturation of water and gas were computed one by one. Seven cases of model test using parallel plates for a single fracture were performed in order to obtain the characteristic equation of relative permeability which would be used in the numerical model. it was difficult to match the characteristic curves of relative permeability from the model tests with the existing emperical equations, consequently a logistic equation was proposed. As the equation is composed of the parameters involving aperture size, it can be applied to any fracture.

• Journal of Wetlands Research
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• v.14 no.4
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• pp.637-644
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• 2012

The discharge estimation that means the most important element in a wetlands ecosystem and rivers is a prime concern. All the interim, this discharge estimation depends on stage-discharge curve, but the limitation of stage-discharge curve that uses only connection between the stage and discharge is widely well known. Thus, this paper proposed a method of discharge estimation in a section through "representative parameter estimation method" by using Manning and Chezy equations that have been extensively used in an open channel. Each result is presented by both RMSE and Discrepancy Ratio. The scale difference for the results between laboratory and natural open channel data existed, but the each result showed that the estimated discharge agree with the measured discharge. If the verification and improvement are conducted in various rivers through continuous study, the easy and rapid discharge estimation will be possible. So, the proposed method will be utilized in the water resources fields.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.4
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• pp.307-314
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• 1998

A novel high power factor Dual Half Bridge Series Resonant Inverter (DHB-SRI) for an induction heating appliance with multiple loads is proposed to remove the interferential acoustic noise caused by the difference between operating frequencies of adjacent loads. The circuit enables independent full power range control of two induction heating elements by one inverter circuit and has minimum switching losses due to the zero voltage switching characteristic. According to the mode analysis, I will explain the operation of the proposed circuit. To evaluate the required cooling capacity, loss analysis is performed through deriving some loss equations. In order to obtain the power factor correction capability and to lessen the system size, suitable design guides are given. Using the designed values, the proto-type circuit with 2.8kW power consumption for each induction heating element is built and tested to verify the operation of the proposed circuit.

• Journal of Biosystems Engineering
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• v.42 no.1
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• pp.44-55
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• 2017

Background: Heat recovery is one of the prominent ways to save a considerable amount of conventional fossil fuel and minimize its adverse effects on the environment. The rotary heat exchanger is one of the most effective and efficient devices for heat recovery or heat exchanging purposes. It is a regenerative type of heat exchanger, which has been studied and used for many heat recovery purposes. However, regenerative thermal wheels have been mostly used as heat recovery systems in buildings. For modeling a rotary regenerator, it is very important to numerically consider all the factors involved, such as effectiveness, rotational speed, geometrical size and shape, and pressure drop (${\Delta}p$). In recent times, several researchers have actively studied the rotary heat exchangers, both theoretically and experimentally. Reviews: In this paper different advances in the numerical modeling of regenerative rotary heat exchangers in relation to fluid flow and heat transfer have been discussed. Researchers have indicated that the effectiveness of the regenerative rotary heat exchanger depends on various factors including, among many others, rotational speed, rotational period and combustion power. It is reported that with the increase of periodic rotation the deviation of theoretical results from the experimental result increases. The available literature indicates that regenerative heat exchangers are having relatively more effectiveness (60-80%), compared to other heat exchangers. It is also observed that the finite difference method and finite volume methods are mostly used for discretizing the heat transfer governing equations, under some assumptions. Research also indicates that for the effectiveness calculation the ${\varepsilon}-NTU$ method is the most popular and convenient.

• International Journal of Highway Engineering
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• v.2 no.1
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• pp.147-156
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• 2000

Compaction is known to critically affect pavement performance. Due to its importance, a theoretical modelling of compacted density in the term of number of roller coverages is attempted by assuming compaction process essentially identical to pavement rutting. Excellent data fittings by the developed equation may prove the validation of assumptions made as well as justification of its use. According to the derived equation, a plot of density difference with respect to number of roller coverages in the logarithmic scale Produces a linear relationship. However, this linearity is turned out to be deviated by cooling effect, change of amplitude and frequency. Investigation of these three factors proposes a new generalized compaction density equation, which shows a promising future. By applying this general formula, the equations for the number of roller coverages required and the final compaction density obtained for a particular compaction project is derived first time in compaction research.