• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.135-138
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• 1996

A wide angle propagation techinque is formulated through an expansion of the Holmholtz operator followed by a Pade expansion and factorization of the resulting polynomials. Its accuracy is checked through the successful modeling of integrated waveguide turning mirrors, indicating that 6-th order polynomial can handle as large as 55$^{\circ}$tilt angle very accurately.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.659-663
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• 2010

In recent, flood inundation damages by hydraulic structure failures have increased drastically and thus a variety of countermeasures were needed to minimize such damages. A real-time flood inundation prediction technique is essential to protect and mitigate flood inundation damages. In the context of real time flood inundation modeling, this study aims to develop a grid based two-dimensional numerical method for flood inundation modeling using globally-available DEM data: SRTM with $90m{\times}90m$ spatial resolution. The newly-developed model guarantees computational efficiency in terms of geometric data processing by direct application of DEM for flood inundation modeling and also have good compatibility with various types of raster data when compared to a commercial model such as FLUMEN. The model, which employed the leap-frog algorithm to solve shallow water and continuity equations, can simulate inundating flow from channel to lowland and also returning flow from lowland to channel by comparing water levels between channel and lowland in real time. We applied the model to simulate the BaekSan levee break in the Nam river during a flood period from August 10 to 13, 2002. The simulation results had good agreements with the field-surveyed data in terms of inundated area and also showed physically-acceptable velocity vector maps with respect to inundating and returning flows.

• Computers and Concrete
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• v.32 no.3
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• pp.339-349
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• 2023

Fast-built construction is a key feature for successful applications of precast concrete (PC) moment frame system in recent construction practices. To this end, by introducing some unique splicing details in precast connections, especially between PC columns including panel zones, use of temporary supports and bracings can be minimized based on their self-sustaining nature. In addition, precast wide beams are commonly adopted for better economic feasibility. In this study, three self-sustaining precast concrete (PC) wide beam-column connection specimens were fabricated and tested under reversed cyclic loadings, and their seismic performances were quantitatively evaluated in terms of strength, ductility, failure modes, energy dissipation and stiffness degradation. Test results were compared with ASCE 41-17 nonlinear modeling curves and its corresponding acceptance criteria. On this basis, an improved macro modeling method was explored for a more accurate simulation. It appeared that all the test specimens fully satisfy the acceptance criteria, but the implicit joint model recommended in ASCE 41-17 tends to underestimate the joint shear stiffness of PC wide beam-column connection. While, the explicit joint model along with concentrated plastic hinge modeling technique is able to present better accuracy in simulating the cyclic responses of PC wide beam-column connections.

• Proceedings of the IEEK Conference
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• 2001.06b
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• pp.133-136
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• 2001

A new package design method to reduce resonance effect due to an IC package is represented. Frequency-variant circuit model of the power/ground plane was developed to accurately reflect the resonance. The circuit model is benchmarked with a full wave simulation, thereby verifying its accuracy. Then it was shown that the proposed technique can efficiently reduce the resonance due to the IC package.

• Journal of the Optical Society of Korea
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• v.10 no.4
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• pp.174-177
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• 2006

We propose a new technique to minimize gain-transient time of wavelength-division-multiplexing (WDM) signals in erbium-doped fiber amplifiers (EDFA) in channel add/drop networks. We have dramatically reduced the gain-transient time to less than $3{\mu}sec$ by applying, for the first time to our knowledge, a disturbance observer with a proportional/integral/differential (PID) controller to the control of EDFA gain. The $3{\mu}sec$ gain-transient time is the fastest one ever reported and it is approximately less than 1.5% of $200{\mu}sec$ gain-transient time of commercially available EDFAs for WDM networks. We have demonstrated the superiority of the new technique by performing the simulation with a numerical modeling software package such as the $Optsim^{TM}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.1
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• pp.28-38
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• 2009

Numerical simulation is performed for microdroplet deposition on a pre-patterned micro-structure. The liquid-air interface is tracked by a level-set method, which is improved by incorporating a sharp-interface modeling technique for accurately enforcing the matching conditions at the liquid-gas interface and the no-slip condition at the fluid-solid interface. The method is further extended to treat the contact angle condition at an immersed solid surface. The present computation of a patterning process using microdroplet ejection demonstrates that the multiphase characteristics between the liquid-gas-solid phases can be used to improve the patterning accuracy.

• Journal of Korea Game Society
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• v.7 no.2
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• pp.11-20
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• 2007

This paper proposes a real-time simulation technique for thin shells undergoing large deformation. Shells are thin objects such as leaves and papers that can be abstracted as 2D structures. Development of a satisfactory physical model that runs in real-time but produces visually convincing animation of thin shells has been remaining a challenge in computer graphics. Rather than resorting to shell theory which involves the most complex formulations in continuum mechanics, we adopt the energy functions from the discrete shells proposed by Grinspun et al. For real-time integration of the governing equation, we develop a modal warping technique for shells. This new simulation framework results from making extensions to the original modal warping technique which was developed for the simulation of 3D solids. We report experimental results, which show that the proposed method runs in real-time even for large meshes, and that it can simulate large bending and/or twisting deformations with acceptable realism.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.204-207
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• 2005

A reliable and practical finite element modeling technique to predict the lifetime of automotive electronics is important for engineers in reliability. In reliability evaluation on the automotive electronics, most studies rarely used FE model verification process. The material properties and boundary conditions are very important factors in this process to assure the reliability of the automotive electronics. This study aims to develop a better and more accurate FE model in order to predict fatigue life of the automotive electronics using Virtual Qualification lifetime assessment techniques. After conducting the modal analysis by the experiments to grasp a system characteristic, this paper presents material properties and boundary conditions that is obtained by the comparisons of FEA simulation results using DOE technique and the experiment results.

• Journal of Power Electronics
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• v.17 no.2
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• pp.442-452
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• 2017

This paper deals with the input-output modeling of a vector controlled PMSM drive system and design of a simple multiple model adaptive control (MMAC) scheme with desired transient responses. We present a discrete-time modeling technique using closed-loop identification that can experimentally identify the equivalent models in the d-q coordinates. A bank of linear models for the equivalent plant of the current loop is first obtained by identifying them at several operating points of the current to account for nonlinearity. Based on these models, we suggest a simple q-axis MMAC combined with a fixed d-axis controller. After the current controller is designed, another equivalent model including the current controller in the speed control loop shall be similarly obtained, and then a fixed speed controller is synthesized. The proposed approach is demonstrated by experiments. The experimental set up consists of a surface mounted PMSM (5 KW, 220V, 8 poles) equipped with a flywheel load of 220kg and a digital controller using DSP (TMS320F28335).

• Nuclear Engineering and Technology
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• v.47 no.5
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• pp.546-558
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• 2015

Chord length sampling method in Monte Carlo simulations is a method used to model spherical particles with random sampling technique in a stochastic media. It has received attention due to the high calculation efficiency as well as user convenience; however, a technical issue regarding boundary effect has been noted. In this study, after analyzing the distribution characteristics of spherical particles using an explicit method, an alternative chord length sampling method is proposed. In addition, for modeling in finite media, a correction method of the boundary effect is proposed. Using the proposed method, sample probability distributions and relative errors were estimated and compared with those calculated by the explicit method. The results show that the reconstruction ability and modeling accuracy of the particle probability distribution with the proposed method were considerably high. Also, from the local packing fraction results, the proposed method can successfully solve the boundary effect problem. It is expected that the proposed method can contribute to the increasing of the modeling accuracy in stochastic media.