• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.99-102
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• 2006

Optimal flow-field design of bipolar-plates for a commercial class PEM(polymer electrolyte membrane) fuel cell stack was carried out on the basis of three-dimensional computational fluid dynamics(CFD) simulation. A three-dimensional CFD model originally developed by Shimpalee et al., has been utilized for performing large-scale simulation of a single fuel cell consisting of bipolar-plates gas diffusion layers, and a membrane-electrode-assembly(MEA). The CFD model is able to predict the current density, pressure drops, gas velocities, vapor and liquid water contents, temperature distributions, etc. inside a single fuel cell. Depending on simulation results from the CFD modeling of a PEM fuel cell, several flow-fields of bipolar-plates were designed and verified. The final design of the bipolar-plate has been chosen from the simulations and experimental tests and showed the best performance as expected from the simulation results under a normal operating condition. Thus, the CFD simulation approach to design the optimal flow-field of the bipolar-plates was successful. The final design was adopted as the best flow-field to build a commercial scale PEM fuel cell stack, the performance of which shows about 42% higher than that of the older bipolar-plate design.

• Structural Engineering and Mechanics
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• v.73 no.5
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• pp.565-584
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• 2020

The nonlinear thermo-electro-elastic buckling behavior of viscoelastic nanoplates under magnetic field is investigated based on nonlocal elasticity theory. Employing nonlinear strain-displacement relations, the geometrical nonlinearity is modeled while governing equations are derived through Hamilton's principle and they are solved applying semi-analytical generalized differential quadrature (GDQ) method. Eringen's nonlocal elasticity theory considers the effect of small size, which enables the present model to become effective in the analysis and design of nano-sensors and nano actuators. Based on Kelvin-Voigt model, the influence of the viscoelastic coefficient is also discussed. It is demonstrated that the GDQ method has high precision and computational efficiency in the buckling analysis of viscoelastic nanoplates. The good agreement between the results of this article and those available in literature validated the presented approach. The detailed mathematical derivations are presented and numerical investigations are performed while the emphasis is placed on investigating the effect of the several parameters such as electric voltage, small scale effects, elastomeric medium, magnetic field, temperature effects, the viscidity and aspect ratio of the nanoplate on its nonlinear buckling characteristics. It is explicitly shown that the thermo-electro-elastic nonlinear buckling behavior of viscoelastic nanoplates is significantly influenced by these effects. Numerical results are presented to serve as benchmarks for future analyses of viscoelastic nanoplates as fundamental elements in nanoelectromechanical systems.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.32-41
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• 2009

In this study, scale-down design of full-scale Korean Utility Helicopter (KUH) main rotor blade has been investigated. The scaled model system were designed for the measurement of aerodynamic performance, tip vortex and noise source. For the purpose of considering the same aerodynamic loads, the Mach-scale method has been applied. The Mach-scaled model has the same tip Mach number, and it also has the same normalized frequencies. That is, the Mach-scaled model is analogous to full-scale model in the view point of aerodynamics and structural dynamics. Aerodynamic scale-down process could be completed just by adjusting scaling dimensions and increasing rotating speed. In the field of structural dynamics, design process could be finished by confirming the rotating frequencies of the designed blade with the stiffness and inertial properties distributions produced by sectional design. In this study, small-scaled blade sectional design were performed by applying domestic composite prepregs and structural dynamic characteristics of designed model has been investigated.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.1
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• pp.40-48
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• 2007

This paper presents a novel texture segmentation method using multilayer perceptron (MLP) networks and Markov random fields in multiscale Bayesian framework. Multiscale wavelet coefficients are used as input for the neural networks. The output of the neural network is modeled as a posterior probability. Texture classification at each scale is performed by the posterior probabilities from MLP networks and MAP (maximum a posterior) classification. Then, in order to obtain the more improved segmentation result at the finest scale, our proposed method fuses the multiscale MAP classifications sequentially from coarse to fine scales. This process is done by computing the MAP classification given the classification at one scale and a priori knowledge regarding contextual information which is extracted from the adjacent coarser scale classification. In this fusion process, the MRF (Markov random field) prior distribution and Gibbs sampler are used, where the MRF model serves as the smoothness constraint and the Gibbs sampler acts as the MAP classifier. The proposed segmentation method shows better performance than texture segmentation using the HMT (Hidden Markov trees) model and HMTseg.

• Journal of Korea Technology Innovation Society
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• v.8 no.3
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• pp.932-954
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• 2005

The purpose of this paper is to evaluate of The University of Science and Technology (UST) as field-oriented graduate school model. The UST is unique in world-wide because of its operating system through the synergy effect of research and education and its interdisciplinary major system differentiated from the traditional graduate school, It first deals with measuring the users satisfaction by using a five-point Likert scale to analyze the general and special factors of UST, through which some findings are pointed out as follows; the education aims and visions are highly satisfied while essential factors in field-oriented education such as curriculum composition, apprentice and tailored education system, field training are not so high level. Finally it points out some suggestions for the UST development.

• Advances in nano research
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• v.15 no.5
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• pp.485-493
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• 2023

Critical multi-field loads and free vibration responses of the sandwich piezoelectric/piezomagnetic microplate subjected to combination of magnetoelectromechanical loads based on a thickness-stretched higher order shear deformable model using Hamilton's principle. The lateral displacement is assumed summation of bending, shearing and stretching functions. The elasti core is sandwiched by a couple of piezoelectric/piezomagnetic face-sheets subjected to electromagnetocmechanical loads. The work of external force is calculated with considering the in-plane mechanical, electrical and magnetic loads based on piezomagnetoelasticity relations. The critical multi field loading and natural frequency analysis are performed to investigate influence of geometric and loading parameters on the responses. A verification is performed for justification of the numerical results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.2 no.2
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• pp.68-74
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• 2010

The development of a numerical model using the fractional area/volume obstacle representation (FAVOR) method for predicting a nearshore current field bounded by complicated geometric shapes, and a three-dimensional (3D) beach evolution was described in this article. The 3D model was first tested against three cases to simulate the nearshore current fields around coastal structures, a river mouth, and a large scale cusp bathymetry. Then, the morphodynamic model tests, which are adopting the nearshore current model, were applied for the computations of beach evolution around a detached breakwater and two groins. It was confirmed that the presented model associated with the FAVOR method was useful to predict the nearshore current field in the vicinity of the complicated geometric shapes. Finally, the model was applied to a tombolo formation in a field site of Kunnui fishery port, which is located in Hokkaido, Japan.

• Journal of Environmental Science International
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• v.4 no.2
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• pp.159-168
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• 1995

To predict reasonably the movement and the concentration of the pollutants in the coastal area. A simulation model should be prepared considering detail topography with land-sea and the urban effects, and the resolution near the source. The explicit method can not be applied due to the instability of the numerical calculation in high horizontal-grid resolution, while the ADI scheme satisfied with the high horizontal grid resolution and can be used in the fine mesh system which shows the detail topography, atmospheric flow The ADI method which studied the high horizontal grid resolution was excellent. The two dimensional model used in the study using ADI method is proved as a reasonable model to predict the wind field in any small scale area including mountainous coastal urban area.

• Journal of Ocean Engineering and Technology
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• v.34 no.2
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• pp.128-135
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• 2020

When high waves and storm surge strike simultaneously, the characteristics of the fluid field change drastically from overtopping according to the wave runup height to overflow through a transition state that combines overtopping and overflows. However, an estimation model or evaluation method has not yet been established because there is not enough engineering data. This study developed a wave overtopping-overflow transition model based on a full-scale experiment involving wave overtopping and overflow transition, which appropriately reproduced the effect of waves or the temporal change in inundation flow. Using this model to perform a calculation for the wave overtopping and overflow transition process under typical circumstances, this study determined the wave runup height and features of the inundation flow under time series changes as an example.

• Computers and Concrete
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• v.25 no.4
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• pp.343-354
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• 2020

In this paper, vibration characteristics of chiral double-walled carbon nanotubes entrenched on Kelvin's model. The Eringen's nonlocal elastic equations are being combined with Kelvin's theory to observe small scale response. A nonlocal model has been formulated to explore the frequency spectrum of chiral double-walled CNTs along with diversity of indices and nonlocal parameter. Wave propagation is proposed technique to establish field equations of model subjected to four distinct end supports. The significance of scale effect in relevance of length-to-diameter and thickness- to- radius ratios are discussed and displayed in detail.