• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.22 no.2
• /
• pp.487-495
• /
• 2021

The voltages mainly used in ships are 450 [V], 6.6 [kV], and 11 [kV], and an earthed system is applied to ensure the stability of the power distribution system. In general, low-voltage ships using 450 [V] apply an unearthed system, while high-voltage ships using 6.6 [kV] or 11 [kV] use a high-resistance earthed system. When an earth fault occurs in a ship's power distribution system, the voltage of the healthy phase increases to the line-to-line voltage or higher, which causes an excessive impact on the insulation of the cable. Thus, analyzing this behavior is very important. In this paper, we investigate the characteristics of the line-to-earth voltage variation according to earth faults and a recognition procedure of a faulty phase using the symmetrical coordinate method for a high-resistance earthed system and unearthed system. A mathematical model of the line-to-earth voltage was derived through the symmetric coordinate method, and the ship voltage for simulations was selected as 6.6 [kV] and 450 [V]. A MATLAB simulation proved that this method can determine the highest increase of the line-to-earth voltage, which leads by 120° on the faulty phase, and it accurately judges the faulty phase in both earthed systems.

• The Journal of the Convergence on Culture Technology
• /
• v.8 no.1
• /
• pp.441-452
• /
• 2022

Training using metacognition in a learning environment is one of the topics that have been continuously studied since the 1990s. Metacognition can be broadly divided into declarative metacognitive knowledge and procedural metacognitive knowledge (metacognitive skills). Accordingly, metacognitive training has also been studied focusing on one of the two metacognitive knowledge. The purpose of this study was to examine the role of metacognitive skills training in the context of mathematical problem solving. Specifically, the learner performed the prediction of problem difficulty, estimation of problem solving time, and prediction of accuracy in the context of a test in which problems of various difficulty levels were mixed within a set, and this was repeated 5 times over a total of 5 weeks. As a result of the analysis, we found that there was a significant difference in all three predictive indicators after training than before training, and we revealed that training can help learners in problem-solving strategies. In addition, we analyzed whether there was a difference between the experiment group and control group in the degree of test anxiety and math achievement. As a result, we found that learners in the experiment group showed less emotional and relationship anxiety at 5 weeks. This effect through metacognitive skill training is expected to help learners improve learning strategies needed for test situations.

• Knowledge Management Research
• /
• v.22 no.4
• /
• pp.237-260
• /
• 2021

This study aims to make suggestions for more effective budget utilization and R&D project investment through verification of the efficiency of research results for the government's R&D projects. Efficiency was analyzed using Data Envelope Analysis(DEA) and 'Malmquist Index analysis' for the research results of convergence research projects organized by the National Science and Technology Research Association. The analysis targets were convergence research projects organized by the National Science and Technology Research Association and general entrusted research projects by government-funded research institutes, and dynamic analysis was conducted using DEA and Malmquist Index analysis. As a result of the analysis, the convergence research project showed high efficiency from the static perspective of DEA. On the other hand, from a dynamic perspective through the Malmquist Index analysis method, the efficiency of the general consignment project gradually declined, while the efficiency of the convergence research project improved every year. This suggests that convergence studies have higher results than general studies. Through the results of this study, we intend to present objective standards for performance evaluation of government R&D investment and provide objective implications for rational investment policies and research project planning of research personnel and research funds to improve efficiency for government-funded research institutes.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.28 no.4
• /
• pp.620-631
• /
• 2022

This paper shows the numerical prediction of the change in oil outflow rate according to the orifice shape of a damaged ship by using the computational fluid dynamics (CFD) analysis method. It also provides discharge coefficients for various orifice shapes to be used in theoretical prediction approaches. The oil outflow from the model ship was analyzed using a multiphase flow method under the condition that the Froude and Reynolds number similitudes were satisfied. The present numerical results were verified by comparing them with the available experimental data. Along with the aspect ratio of the orifice and the wall thickness of the cargo tank, the effects of the orifice shapes defined by mathematical figures on the oil outflow were investigated. To consider more realistic situations, the investigation of the ef ect of the crushed iron plate around the damaged part was also included. The numerical results confirmed the change in oil outflow time for various shapes of the damaged part of the oil tank, and discharge coefficients that quantify the viscous effects of those orifice shapes were extracted. To verify the predicted discharge coefficients, they were applied to an oil spill estimation equation. As a result, a good agreement between the CFD and theoretical results was obtained.

• Journal of the Korea Society for Simulation
• /
• v.31 no.1
• /
• pp.29-41
• /
• 2022

As one of the alternatives to solve the problem of unstable food supply and demand imbalance caused by abnormal climate change, the need for plant factories is increasing. Airflow in plant factory is recognized as one of important factor of plant which influence transpiration and heat transfer. On the other hand, Digital Twin (DT) is getting attention as a means of providing various services that are impossible only with the real system by replicating the real system in the virtual world. This study aimed to develop a digital twin model for airflow prediction that can predict airflow in various situations by applying the concept of digital twin to a plant factory in operation. To this end, first, the mathematical formalism of the digital twin model for airflow analysis in plant factories is presented, and based on this, the information necessary for airflow prediction modeling of a plant factory in operation is specified. Then, the shape of the plant factory is implemented in CAD and the DT model is developed by combining the computational fluid dynamics (CFD) components for airflow behavior analysis. Finally, the DT model for high-accuracy airflow prediction is completed through the validation of the model and the machine learning-based calibration process by comparing the simulation analysis result of the DT model with the actual airflow value collected from the plant factory.

• Particle and aerosol research
• /
• v.18 no.1
• /
• pp.9-21
• /
• 2022

In this study, a novel antiviral coating method for the air filtration system of subway station was investigated. Using dry aerosol coating process, we developed a high-performance antiviral air filter with spark discharger and carbon brush type ionizer. Silver nanoparticles were produced by a spark discharge generation system with ion injection system and were used as antiviral agents coated onto a medium grade air filter. The pressure drop, filtration efficiency, and antiviral ability of the filter against aerosolized MS2 virus particles as a surrogate of SARS-CoV-2 virus were tested with dust contamination. Dust contamination caused the increase of the filtration efficiency and pressure drop, while the antiviral agents (in this study, silver nanoparticles) coating did not have any significant effect on the filtration efficiency and pressure drop. Using these properties, we suggested a novel method to maximize the antiviral performance of the antiviral air filter that was contaminated by dust particles. Moreover theoretical analysis of antiviral ability with dust contamination and re-coated antiviral agents was carried out using a mathematical model to calculate the time-dependent antiviral effect of the filter under actual conditions of subway station. Our model can be used to apply on antiviral air filtration system of subway station for prevention of pandemic diffusion, and predict the life cycle of an antiviral filter.

• Tunnel and Underground Space
• /
• v.31 no.6
• /
• pp.480-493
• /
• 2021

Since the generalized Hoek-Brown criterion (GHB) provides an efficient way of identifying its strength parameter values with the consideration of in-situ rock mass condition via Geological Strength Index (GSI), this criterion is recognized as one of the standard rock mass failure criteria in rock mechanics community. However, the nonlinear form of the GHB criterion makes its mathematical treatment inconvenient and limits the scope of its application. As an effort to overcome this disadvantage of the GHB criterion, the explicit approximate analytical equations for the minimum principal stress, which is associated with the maximum principal stress at failure, are formulated based on the Taylor polynomial approximation of the original GHB criterion. The accuracy of the derived approximate formula for the minimum principal stress is verified by comparing the resulting approximate minimum principal stress with the numerically calculated exact values. To provide an application example of the approximate formulation, the equivalent friction angle and cohesion for the expected plastic zone around a circular tunnel in a GHB rock mass are calculated by incorporating the formula for the approximate minimum principal stress. It is found that the simultaneous consideration of the values of mi, GSI and far-field stress is important for the accurate calculation of equivalent Mohr-Coulomb parameter values of the plastic zone.

• The Journal of the Korea Contents Association
• /
• v.22 no.6
• /
• pp.629-637
• /
• 2022

It is at risk of depletion of biodiversity due to indiscriminate overfishing of ecosystems and destruction of habitats. Intensive fertilizers or development of related facilities to increase agricultural production in poor indigenous areas devastate the soil. Preservation of biodiversity is now emerging as an important issue of global human coexistence. After the Post-2020 GBF Declaration, all governance in agricultural development in indigenous agricultural areas should be supported and promoted as biodiversity conservation measures. A compromise plan to reduce ecosystem development and biodiversity loss can help establish public governance policies. In this paper, a viability kernel used for viable control feedback analysis is introduced to solve conflicting economic and ecological problems in ecosystem conservation, and a mathematical model on biodiversity conservation by the viability kernel is examined. Because all species in the ecosystem are interdependent, if the balance is broken, biodiversity is depleted, which is irreversible and eventually leads to extinction. For sustainable use and harmony of biological resources, a lot of policy consideration is required, such as creative governance that can efficiently protect all species. Subsidies or tax incentives have a direct impact on biodiversity conservation. The recovery of species in a state of decreasing biodiversity can be said to be of great economic value. Biodiversity will allow indigenous producers to be proud of their unique traditional knowledge and have a positive impact on local tourism, thereby enhancing regional identity and greatly contributing to the survival and prosperity of mankind.

• Industry Promotion Research
• /
• v.7 no.1
• /
• pp.59-74
• /
• 2022

There are three main ways to interpret Zhouyi(周易). The first is to interpret it as a number, the second is to interpret it as an image symbolized by the Gwae(卦), and the third is to interpret it as the moral reason contained in it. Although YulRyeo(律呂) is not as widely known as Zhouyi, its use in ancient times was the same as that of the main character. First, the mathematical analysis method using the three-pronged method for tuning musical instruments, second, the symbolic interpretation using the musical meaning symbolized by YulRyeo, and third, the applied interpretation method that expands to the moral reason contained in YulRyeo. The purpose of this thesis is to organize the dictionary meaning of YulRyeo and various meanings of ancient YulRyeo. In addition, by studying ancient literature on the meaning of YulRyeo's magic spell mechanics(術數易學) and Naepeum and Five Elements(納音五行), which is the origin of Gobeop Myongriology, I classify and interpret them in detail. and to find ways to apply it to Myongriology. It is hoped that this study will give a more in-depth understanding of YulRyeo and will be of little help to related studies such as the mechanics of magic and Myongriology studies in the future.

• Education of Primary School Mathematics
• /
• v.25 no.4
• /
• pp.313-328
• /
• 2022

The purpose of this study is to understand the characteristics of the questions presented in shapes area and Measurement area of elementary mathematics textbooks. For this purpose, the types of questions presented in shapes area and measurement area of elementary mathematics textbooks and their working functions were comparatively analyzed by area and by grade cluster. As a result of the analysis, the number of questions per lesson increased sharply in the 3rd and 4th grade cluster compared to the 1st and 2nd grade cluster in both shapes area and measurement area. In these two areas, the most common reasoning questions are presented. It is presented relatively more in measurement area than in shapes area. There was a clear difference between the types of questions presented in shapes area and measurement area. In common with the two areas, questions mainly were acted as a function to help students learn to reason mathematically, a function to help students to determine whether something is mathematically correct, and a function to help students learn to conjecture, invent, and solve problem. The characteristics of the questions identified in this study can provide teaching/learning implications for the design and application of the questions suitable for the guidance of shapes area and measurement area, and can be used as a reference material when writing mathematics textbooks.