• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.1
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• pp.40-47
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• 2017

In this paper, a small signal model for grid-connected inverter with unipolar pulse width modulation method is presented. Small-signal analysis allows to predict the stability and dynamics of the inverter. To regulate output voltage and to achieve power factor correction, inverter has two control loops. Loop gains are useful to identify the stability for multi-loop controlled system. Based on small-signal model, controllers are designed to improve audio susceptibility and output impedance characteristics. Proposed small-signal model and controllers are verified by PSIM simulation and experiments.

• Journal of Hydrogen and New Energy
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• v.35 no.4
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• pp.437-450
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• 2024

Sustainable shipping depends on eco-friendly energy solutions. This paper reviews methods for predicting marine fuel cell performance, including empirical approaches, physical modeling, data-driven techniques, and hybrid methods. Accurate prediction models tailored to the marine environment's unique conditions are crucial for operational efficiency. By evaluating the strengths and weaknesses of each method, this study provides a comprehensive analysis of effective strategies for forecasting polymer electrolyte membrane fuel cell and solid oxide fuel cell performance in marine applications. These insights contribute to the advancement of eco-friendly shipping technologies and enhance fuel cell performance in challenging marine environments.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.430-437
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• 2000

Fertilizer impaction mechanism was simulated using a commercial program RecurDyn$^{(R)}$ a dynamic program that could handle contact problems. Even if there had been numerous papers on modeling of fertilizer applicator, the performance predictions were not satisfactory due to simplification in modeling. The most significant simplification was assumption of fertilizer particles as a solid particle. The assumption would eliminate rotation of fertilizer particles during the impaction mechanism. However, impaction of rotating body would be different from that of a solid particle. This paper introduced how the impaction was modeled using RecurDyn$^{(R)}$. In order to simulate, restitution coefficient and contact time was measured. A stiffness coefficient and a damping coefficient of a fertilizer was theoretically estimated using the measured data. Validity of the simulation result was not proved yet, but judged to be promising.ged to be promising.ing.

• Korean Journal of Computational Design and Engineering
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• v.15 no.3
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• pp.243-252
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• 2010

This paper describes a new practical simplification method for feature-based solid models. In this approach, a solid model created using feature modeling operations is first simplified by the suppression of detailed features, and then, if necessary, the model is converted to a surface model to facilitate its modification. Finally, the simplified surface model is delivered to analysis packages. The algorithm was implemented based on CATIA V.5 and applied to mid-surface generation of plastic parts for structural analysis to prove the validity and usefulness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.4
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• pp.331-340
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• 1982

Numerical analysis is made on the turbulent heat transfer with suspension of solid particles in circular tube with constant heat flux. The mean motion of suspending particles in mixture is treated as the secondary gas flow with virtual density and viscosity. Our modeling of turbulent transport phenomena of suspension flow is based on this assumption and conventional mixing length theory. This paper gives the evidence that the mixing length models can be extended to close the governing equations for two phase turbulent flow with solid boundary at a first order level. Results on Nusselt numbers obtained by analytical treatments are compared with available experimental data and discussed. They suggest that the most important parameters of two phase turbulent heat transfer phenomena are relative particle diameter to pipe diameter, gas-solid loading ratio, and specific heat of suspending material.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.175-178
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• 2008

A Numerical Simulation which uses preconditioning algorithm to examine unsteady combustion processes for the AP/HTPB propellant with a converging-diverging nozzle has been compared with experimental data for solid rocket motor. To analysis reacting flow of solid rocket motor, unsteady pressure, temperature contour was simulated by grid moving of propellant.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.4 no.2
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• pp.193-198
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• 2004

This paper describes an automatic finite element (FE) mesh generation for three-dimensional structures consisting of tree-form surfaces. This mesh generation process consists of three subprocesses: (a) definition of geometric model, (b) generation of nodes, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Node is generated if its distance from existing node points is similar to the node spacing function at the point. The node spacing function is well controlled by the fuzzy knowledge processing. The Voronoi diagram method is introduced as a basic tool for element generation. Automatic generation of FE meshes for three-dimensional solid structures holds great benefits for analyses. Practical performances of the present system are demonstrated through several mesh generations for three-dimensional complex geometry.

• Journal of the Korean Institute of Intelligent Systems
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• v.15 no.3
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• pp.343-348
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• 2005

This paper describes an automatic finite element (FE) mesh generation for three-dimensional structures consisting of free-form surfaces. This mesh generation process consists of three subprocesses: (a) definition of geometric model, i.e. analysis model, (b) generation of nodes, and (c) generation of elements. One of commercial solid modelers is employed for three-dimensional solid structures. Node is generated if its distance from existing node points is similar to the node spacing function at the point. The node spacing function is well controlled by the fuzzy knowledge processing. The Delaunay method is introduced as a basic tool for element generation. Automatic generation of FE meshes for three-dimensional solid structures holds great benefits for analyses. Practical performances of the present system are demonstrated through several mesh generations for three-dimensional complex geometry.

• Advances in aircraft and spacecraft science
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• v.9 no.5
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• pp.479-491
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• 2022

This work concerns the investigation of a Q1D methodology employed to study pressure oscillations in solid rocket motors driven by hydrodynamic instabilities. A laboratory-scale solid motor designed to develop vortex-shedding phenomena is analyzed for the whole firing time. The comparison between numerical results and experimental data shows good agreement regarding pressure oscillations signature, especially in the flute-mode behavior, the typical oscillations frequency trend present in any motor liable to hydrodynamic instabilities. Such result ensures the model capability to cope with this particular kind of pressure oscillations source, allowing the investigation of the phenomenon with a lighter and cost savings methodology than CFD simulations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.220-220
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• 2003