• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.2
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• pp.119-129
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• 2004

A three dimensional (3D) method of analysis is presented for determining the free vibration frequencies and mode shapes of thick, circular and annular plates with nonlinear thickness variation along the radial direction. Unlike conventional plate theories, which are mathematically two dimensional (2D), the present method is based upon the 3D dynamic equations of elasticity. Displacement components u/sub s/, u/sub z/, and u/sub θ/ in the radial, thickness, and circumferential directions, respectively, are taken to be sinusoidal in time, periodic in θ, and algebraic polynomials in the s and z directions. Potential (strain) and kinetic energies of the plates are formulated, and the Ritz method is used to solve the eigenvalue problem thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four digit exactitude is demonstrated for the first five frequencies of the plates. Numerical results we presented for completely free, annular and circular plates with uniform linear, and quadratic variations in thickness. Comparisons are also made between results obtained from the present 3D and previously published thin plate (2D) data.

• Hwankyungkyoyuk
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• v.6 no.1
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• pp.199-209
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• 1994

To investigate the trends in environmental education research of foreign countries, the paper published in the Journal of Environmental Education from 1984 to 1992 were analyzed. Major results of this study are as follows: 1. Total number of the paper analyzed was 178 and the average numbers of paper published per year were similar. 2. Researchers' majors were various. 3. The major targets of the researches in environmental education were school students. 4. Questionnaire was used in many researches and the main area of researches was strategy for environmental education. 5. Major type of research was survey and the main area of researches was strategy for environmental education. 6. The affective domain was highly concerned in environmental education researches.

• Korean Journal of Food Science and Technology
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• v.37 no.6
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• pp.1012-1017
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• 2005

Predictive growth model of putrefactive bacteria of surimi-based imitation crab in the modified surimi-based imitation crab (MIC) broth was investigated. The growth curves of putrefactive bacteria were obtained by measuring cell number in MIC broth under different conditions (Initial cell number, $1.0{\times}10^2,\;1.0{\times}10^3$ and $1.0{\times}10^4$ colony forming unit (CFU)/mL; temperature, $15^{\circ}C,\;20^{\circ}C\;and\;25^{\circ}C$) and applied them to Gompertz model. The microbial growth indicators, maximum specific growth rate constant (k), lag time (LT) and generation time (GT), were calculated from Gompertz model. Maximum specific growth rate (k) of putrefactive bacteria was become fast with rising temperature and fastest at $25^{\circ}C$. LT and GT were become short with rising temperature and shortest at $25^{\circ}C$. There were not significant differences in k, LT and GT by initial cell number (p>0.05). Polynomial model, $k=-0.2160+0.0241T-0.0199A_0$, and square root model, $\sqrt{k}=0.02669$ (T-3.5689), were developed to express the combination effects of temperature and initial cell number, The relative coefficient of experimental k and predicted k of polynomial model was 0.87 from response surface model. The relative coefficient of experimental k and predicted k of square root model was 0.88. From above results, we found that the growth of putrefactive bacteria was mainly affected by temperature and the square root model was more credible than the polynomial model for the prediction of the growth of putrefactive bacteria.

• Korean Journal of Agricultural and Forest Meteorology
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• v.12 no.2
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• pp.122-131
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• 2010

This paper introduces the concept of a virtual ecosystem and reports the following three mathematical approaches that could be widely used to construct such an ecosystem, along with examples: (1) a molecular dynamics simulation approach for animal flocking behavior, (2) a stochastic lattice model approach for termite colony behavior, and (3) a rule-based cellular automata approach for biofilm growth. The ecosystem considered in this study consists of artificial organisms and their environment. Each organism in the ecosystem is an agent that interacts autonomously with the dynamic environment, including the other organisms within it. The three types of model were successful to account for each corresponding ecosystem. In order to accurately mimic a natural ecosystem, a virtual ecosystem needs to take many ecological variables into account. However, doing so is likely to introduce excess complexity and nonlinearity in the analysis of the virtual ecosystem's dynamics. Nonetheless, the development of a virtual ecosystem is important, because it can provide possible explanations for various phenomena such as environmental disturbances and disasters, and can also give insights into ecological functions from an individual to a community level from a synthetic viewpoint. As an example of how lower and higher levels in an ecosystem can be connected, this paper also briefly discusses the application of the second model to the simulation of a termite ecosystem and the influence of climate change on the termite ecosystem.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.5
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• pp.622-630
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• 1998

Rotating Biological Contactor (RBC) was tested for the removal of total ammonia nitrogen (TAN) by using simulated aquaculture system. RBC performance was evaluated by controlling revolution rate of disk and hydraulic residence tile (HRT). The optimum revolution rate of disk was 4 rpm, As HRT of RBC was increased, TAN removal efficiency of RBC and TAN concentration of rearing water were increased. HRT for maintaining lowest TAN concentration of rearing water was 9.5 minutes and at that condition TAN concentration of rearing tank was $1.03 g/m^3$

• Journal of KIISE:Software and Applications
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• v.33 no.8
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• pp.730-740
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• 2006

In recent years, bullied students and rogue groups in teenagers make many serious social problems. In this paper we propose a novel approach that more objectively analyzes peer relationships among students. As the data for objective analysis, we use communication history records that are collected from various communication tools such as telephones, e-mails, and messengers. We use the simple intuition that communication history records implicitly contain peer relationship information. And, we adopt data mining techniques for the more systematic analysis. The proposed peer relationship analysis consists of the following steps. First, we formally define the notion of degree of familiarity between friends, and present mathematical equations that compute the degree based on communication history records. In the proposed method, we use the intuition that the degree of familiarity from student x to student y becomes higher as x makes the more communications with y. Second, by using the degree of familiarity between students, we find out the students who are potentially bullied. This procedure is based on the assumption that a bullied student may have a very small number of history records from other students to him. Third, we adopt the clustering technique, one of the most representative data mining techniques, to find out meaningful student groups by using the degree of familiarity. To use the clustering technique, we formally define the notion of similarity between friends based on the degree of familiarity, and perform clustering using the notion. Last, to show the practicality of the proposed method, we have implemented the method and interpreted the meaning of the experimental results. Overall, we believe that our research result provides an effective framework that analyzes peer relationships more objectively and more systematically.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.1
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• pp.46-51
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• 2014

The most important process of engineering system optimal design is to identify the relationship between the design variables and system response. In case of the system optimization, Response Surface Method (RSM) is widely used. The optimization process of RSM generates the design space using the typical alternative candidates and finds the optimal design point in the generated design space. By changing the optimal point depending on the configuration of the design space, it is important to generate the design space. Therefor in this study, the design space is generated by using the relationship between design variables and system response based on Neuro-Response Surface Method (NRSM). And I try to construct the framework for optimal shape design based on NRSM that the optimum shape can be predicted using the Non-dominated Sorting Genetic Algorithm-II (NSGA-II) within the generated design space. In order to verify the usefulness of the constructed framework, we applied the nonlinear mathematical function problem. In this study, we can solve the constraints of time in the optimization process for the engineering problem and effective to determine the optimal design was possible. by using the generated framework for optimal shape design based on NRSM. In the future research, we try to apply the optimization problem for Naval Architectural & Ocean Engineering based on the results of this study.

• Journal of the Korea Society for Simulation
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• v.20 no.1
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• pp.79-85
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• 2011

The problem of evacuating pedestrians from a room or channel under panic conditions is of obvious importance in daily life. In recent years, several computer models have been developed to simulate pedestrian dynamics. Understanding evacuation dynamics can allow for the design of more comfortable and safe pedestrian facilities. However, these models do not take into account the type and state of mind of pedestrians. They deal with pedestrians as particles and the state of mind as a social force, which is represented by conservative and long-range interactions between individuals. In this study, I used the lattice model proposed in my previous study to explore the evacuation behavior of pedestrians with morality. In this model, three types of pedestrians are considered: adults, children, and injured people. Collisions between adults and children result in injured people. When the number of injured people continuously in contact with each other reaches a given value k, the injured people are removed from the lattice space. This situation is the same as that in which pedestrians start stepping over injured people. This behavior was interpreted as the morality of pedestrians. Simulations showed that the evacuation showed down and eventually became jammed owing to the injured people acting as "obstacles" in relation to the morality k.

• Journal of the Korea Society for Simulation
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• v.29 no.2
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• pp.105-117
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• 2020

Analysis of combat effectiveness is required to consider the concept of tactical cooperative engagement between manned-unmanned weapon systems, in order to predict the required operational capabilities of future weapon systems that meets the concept of 'effect-based synchronized operations.' However, analytical methods such as mathematical and statistical models make it difficult to analyze the effects of complex systems under nonlinear warfare. In this paper, we propose a combat simulation model that can simulate the concept of cooperative engagement between manned-unmanned combat entities based on wireless communications. First, we model unmanned combat entities, e.g., unmanned ground vehicles and drones, and manned combat entities, e.g., combatants and artillery, considering the capabilities required by the future ground system. We also simulate tactical behavior in which all entities perform their mission while sharing battlefield situation information through wireless communications. Finally we explore the feasibility of the proposed model by analyzing combat effectiveness such as target acquisition rate, remote control success rate, reconnaissance lead time, survival rate, and enemy's loss rate under a small-unit armor reconnaissance scenario. The proposed model is expected to be used in war-game combat experiments as well as analysis of the effects of manned-unmanned ground weapons.

• Journal of Korean Elementary Science Education
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• v.25 no.2
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• pp.118-125
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• 2006

The purpose of the study was to research science gifted students' learning styles and perceptions on subject matter content. The data was collected from primary science and mathematics classes of a University Center for Science Gifted Education, science classes of a Metrocity Primary Gifted Education Institute, and classes of a normal school. The results of the study were that gifted students perceived the school curriculum much easier than non-gifted students did, ($X^2(4)=33.180$, p<.001), and that levels of interest in the content did not differ between the groups, but 34.6 percent of the total students responded that they found the content uninteresting. Gifted students did not see the content as being important compared to the non-gifted students, ($X^2(4)=12.443$, p<.05), and gifted students valued the methods used higher than the actual content of the textbook. The most helpful activities for their teaming that gifted students chose were projects, listening to teachers, and conducting experiments, amongst others. They also preformed 'teaming at their own speed in a mixed group'" for the study of social studies, science, and mathematics, whereas non-gifted students preformed teaming at the same speed. The two groups of science gifted students varied especially in their perceptions of most helpful activities. It is suggested that special programs for fulfilling gifted students' needs and abilities need to be developed and implemented.