• Transactions of the Korean hydrogen and new energy society
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• v.32 no.4
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• pp.228-235
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• 2021

Polymer electrolyte membrane fuel cells (PEMFC) are currently being used in various transport applications such as drones, unmanned aerial vehicles, and automobiles. The power required is different according to the type of use, purpose, and the conditions adjusted using a cell stack. The fuel cell stack is compressed to reduce the size and prevent fuel leakage. The unit cells that make up the cell stack are subjected to compression by clamping force, which makes geometrical changes in the porous media and it impacts on cell performance. In this study, finite elements method (FEM) and computational fluid dynamics (CFD) analysis for the deformed unit cell considering the effects of clamping force is performed. First, structural analysis using the FEM technique over the deformed gas diffusion layer (GDL) considering compression is carried out, and the resulting porosity changed in the GDL is calculated. The PEMFC model is then verified by a three-dimensional, two-phase fuel cell simulation applying the physical properties and geometry obtained before and after compression. The detailed simulation results showed different concentration distributions of fuel between the original and deformed geometry, resulting in the difference in the distribution of current density is represented at compressed GDL region with low oxygen concentration.

• Journal of Korean Society on Water Environment
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• v.36 no.6
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• pp.621-635
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• 2020

Water quality models are scientific tools that simulate and interpret the relationship between physical, chemical and biological reactions to external pollutant loads in water systems. They are actively used as a key technology in environmental water management. With recent advances in computational power, water quality modeling technology has evolved into a coupled three-dimensional modeling of hydrodynamics, water quality, and ecological inputs. However, there is uncertainty in the simulated results due to the increasing model complexity, knowledge gaps in simulating complex aquatic ecosystem, and the distrust of stakeholders due to nontransparent modeling processes. These issues have become difficult obstacles for the practical use of water quality models in the water management decision process. The objectives of this paper were to review the theoretical background, needs, and development status of water quality modeling technology. Additionally, we present the potential future directions of water quality modeling technology as a scientific tool for national environmental water management. The main development directions can be summarized as follows: quantification of parameter sensitivities and model uncertainty, acquisition and use of high frequency and high resolution data based on IoT sensor technology, conjunctive use of mechanistic models and data-driven models, and securing transparency in the water quality modeling process. These advances in the field of water quality modeling warrant joint research with modeling experts, statisticians, and ecologists, combined with active communication between policy makers and stakeholders.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.2
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• pp.27-35
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• 2001

Based on the development of mobile communication, the future mobile communication systems are expected to provide higher quality of multimedia services for users than today\`s systems. Therefore, many technical factors are needed in this systems. Especially the secrecy and the safety would be obtained through the introduction of the security for mobile communication. In this paper, we presents a digital nominative proxy signature scheme that processes a user\`s digital signature and encryption using the proxy-agent who has more computational power than origins in mobile communication. The proposed scheme provides non-repudiation and prevents creating illegal signature by the origin and proxy-agent in a phase of proxy signature processing. Also this scheme satisfies the confidentiality and safety in the mobile communication through a confirming signature by the right receiver.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.4
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• pp.1-8
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• 2021

In this paper, we propose an approach that combines the technological advantages of P2P and cloud computing to support MMOGs that allowing a huge amount of users worldwide to share a real-time virtual environment. The proposed P2P system based on cloud computing can provide a greater level of scalability because their more resources are added to the infrastructure even when the amount of users grows rapidly. This system also relieves a lot of computational power and network traffic, the load on the servers in the cloud by exploiting the capacity of the peers. In this paper, we describe the concept and basic architecture of cloud computing-based P2P Systems for scalability of MMOGs. An efficient and effective provisioning of resources and mapping of load are mandatory to realize this architecture that scales in economical cost and quality of service to large communities of users. Simulation results show that by controlling the amount of cloud and user-provided resource, the proposed P2P system can reduce the bandwidth at the server while utilizing their enough bandwidth when the number of simultaneous users keeps growing.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.27 no.3
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• pp.175-180
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• 2021

Although it has recently been regulated for use as an eco-friendly policy in Korea, the use of EPS (Expanded Polystyrene) cooling boxes, which are used as cold chain delivery insulation boxes for fresh agricultural and livestock products, is also increasing rapidly as e-commerce logistics such as delivery have increased rapidly due to COVID-19. Studies were conducted to optimize the EPS cooling container through internal air heat flow of CFD (Computational Fluid Dynamics) analysis and FEM (Finite Element Method) random vibration analysis using domestic PSD (Power Spectral Density) profile of the EPS cooling box to which the refrigerant is applied in this study. In the analysis of the internal air heat flow by the refrigerant in the EPS cooling box, the application of vertical protrusions inside was excellent in volume heat flow and internal air temperature distribution. In addition, as a result of random vibration analysis, the internal vertical protrusion gives the rigid effect of the cooling box, so that displacement and stress generation due to vibration during transport are smaller than that of a general cooling container without protrusion. By utilizing the resonance point (frequency) of the EPS cooling box derived by the Model analysis of ANSYS Software, it can be applied to the insulation and cushion packaging design of the EPS product line, which is widely used as insulation and cushion materials.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.236-245
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• 2021

In this study, direct numerical and large eddy simulations of transitional flows around studs were conducted to investigate the effectiveness of turbulence stimulators at very low speeds for the minimum propulsion power condition of four knots. For simplicity, the studs were assumed to be installed on a flat plate, while the wake was observed up to 0.23 m downstream behind the second stud. For applicability to a model ship, we also studied the flow characteristics behind the first and second studs installed on a curved plate, which was designed to describe the geometry of a bulbous bow. A laminar-to-turbulent transition was observed in the wake at Re_D ≥ 921 (U_∞≥0.290 m/s), and the wall shear stress at Re_D = 1162 (U_∞ = 0.366 m/s) in the second wake was similar to that of the fully developed turbulent boundary layer after a laminar-to-turbulent transition in the first wake. At Re_D = 581 (U_∞ = 0.183 m/s), no turbulence was stimulated in the wake behind the first and second studs on the flat plate, while a cluster of vortical structures was observed in the first wake over the curved plate. However, a cluster of vortical structures was revealed to be generated by the reattachment process of the separated shear layer, which was disturbed by the first stud rather than directly initiated by the first stud. It was quite different from a typical process of transition, which was observed at relatively high Re_D that the spanwise scope of the turbulent vortical structures expanded gradually as it went downstream.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.3
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• pp.183-191
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• 2022

A design method for a propeller type rim-driven axial-flow turbine for a micro-hydropower system is presented. The turbine consists of pre-stator, impeller and post-stator, where the pre-stator plays a role as a guide vane to provide circumferential velocity to the on-coming flow, and the impeller as a rotational power generator by absorbing angular momentum of the flow. BEM(Blade Element Method), which is based on the turbine Euler equation, is employed to design the pre-stator and impeller blades. NACA 66 thickness form and a=0.8 mean camber line, which is widely accepted as a marine propeller blade section, is used for the pre-stator and turbine blade section. A CFD method, derived from the discretization of the RANS equations, is applied for the analysis of the designed turbine system. The design conditions of the turbine is confirmed by the CFD calculation. Turbine characteristic curve is calculated by the CFD method, in order to provide the performance characteristics at off-design operation conditions. The proposed procedures for the design of a propeller type rim-driven axial-flow turbine are established and confirmed by the CFD analysis.

• Journal of Creative Information Culture
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• v.6 no.1
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• pp.31-40
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• 2020

The purpose of this study is to statistically analyze the correlation between block-coding software education and the resilience of elementary school students in order to research the significance of software education. In this study, 61 fourth grade students at an elementary school in Incheon were pre-tested for resilience. A block-coding education program from a nonprofit organization called code.org was used at the learner's level. 15 periods of classes and post-test were conducted to analyze the improvement of resilience. This study finds that control and positivity out of the three parts of resilience(control, positivity, sociality) of the students who took the block-coding classes improved statistically significantly as well as the overall score did too. This suggests that software education can foster not only students' computational thinking skills, but also their resilience, the power to live their lives positively and flexibly.

• Journal of the Institute of Convergence Signal Processing
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• v.22 no.4
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• pp.164-170
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• 2021

Research was conducted to analyze and improve the kinetic performance of offshore wind power generators. The shape used in this study was taken with reference to the previous paper, and the size of the repair area was designed at 80%, 60%, 40%, and 20%, respectively, and the exercise performance was confirmed accordingly. The sea state was calculated in Sea State 4, 5, and 6. In the calculation process, the calculation was performed using commercial computational hydrodynamics (ANSYS) and AQUA. In the case of overall exercise performance, it was confirmed that the smaller the size of the repair area, the smaller the exercise such as heave, roll, and pitch. However, it was confirmed that in the case of a shape in which the size of the repair area was rapidly reduced, there may be cases in which the restoration performance was not satisfied when the restoration calculation was performed. In addition, it was confirmed that there may be an appropriate repair surface depending on the sea condition.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.11
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• pp.4065-4083
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• 2021

Super-resolution can improve the clarity of low-resolution (LR) images, which can increase the accuracy of high-level compute vision tasks. Portable devices have low computing power and storage performance. Large-scale neural network super-resolution methods are not suitable for portable devices. In order to save the computational cost and the number of parameters, Lightweight image processing method can improve the processing speed of portable devices. Therefore, we propose the Enhanced Information Multiple Distillation Network (EIMDN) to adapt lower delay and cost. The EIMDN takes feedback mechanism as the framework and obtains low level features through high level features. Further, we replace the feature extraction convolution operation in Information Multiple Distillation Block (IMDB), with Ghost module, and propose the Enhanced Information Multiple Distillation Block (EIMDB) to reduce the amount of calculation and the number of parameters. Finally, coordinate attention (CA) is used at the end of IMDB and EIMDB to enhance the important information extraction from Spaces and channels. Experimental results show that our proposed can achieve convergence faster with fewer parameters and computation, compared with other lightweight super-resolution methods. Under the condition of higher peak signal-to-noise ratio (PSNR) and higher structural similarity (SSIM), the performance of network reconstruction image texture and target contour is significantly improved.