• Journal of Korean Society for Atmospheric Environment
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• v.32 no.4
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• pp.384-393
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• 2016

In this study, two kinds of industrial filter bags were tested for their filtration performance to apply the existing bag filter systems. Experimental variables were examined for pressure drop, cleaning interval, residual pressure drop, cleaning efficiency, fractional grade efficiency, total collection efficiency according to the filter bag structure. According to these results, the filter bags tested in this study demonstrated good performance in dust collection. This was also true for the double surface filter bag. The lifetime was longer than the round type filter bag because the filtration area was more than 1.6 times wider and the filter quality factor was much higher. Therefore, double surface filter bags are suggested to be used in order to increase filtration performance of the bag filter systems.

• Smart Structures and Systems
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• v.3 no.2
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• pp.133-146
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• 2007

This paper addresses a new type of broad and stage-based hybrid carbon fiber reinforced polymer (HCFRP) sensor that is suitable for the sensing of infrastructures. The HCFRP sensors, a type of composite sensor, are fabricated with three types of carbon tows of different strength and moduli. For all of the specimens, the active materials are carbon tows by virtue of their electrical conductivity and piezoresistivity. The measurement principles are based on the micro- and macro-fractures of different types of carbon tows. A series of experiments are carried out to investigate the sensing performances of the HCFRP sensors. The main variables include the stack order and volume fractions of different types of carbon tows. It is shown that the change in electrical resistance is in direct proportion to the strain/load in low strain ranges. However, the fractional change in electrical resistance (${\Delta}R/R_0$) is smaller than 2% prior to the macrofractures of carbon tows. In order to improve the resistance changes, measures are taken that can enhance the values of ${\Delta}R/R_0$ by more than 2 times during low strain ranges. In high strain ranges, the electrical resistance changes markedly with strain/load in a step-wise manner due to the gradual ruptures of different types of carbon tows at different strain amplitudes. The values of ${\Delta}R/R_0$ due to the fracture of high modulus carbon tows are larger than 36%. Thus, it is demonstrated that the HCFRP sensors have a broad and stage-based sensing capability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.5
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• pp.666-674
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• 2002

A rapid expansion of the moist air or stream through transonic nozzle often leads to not-equilibrium condensation shock, causing a considerable amount of energy loss to the entire flow field. Depending on amount of heat released, condensation shock wave occurs in the nozzle and interacts with the boundary layer flow. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for purpose of alleviation the condensation shock wave in a transonic nozzle. A droplet growth equation is incorporated into two-dimensional wavier-Stokes equation systems. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft transonic wind tunnel is made to validate the present computational results. The results obtained show that the magnitude of condensation shock wave is reduced by the current passive control method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.1
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• pp.269-286
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• 2018

Signal detection in symmetric alpha-stable ($S{\alpha}S$) distributed noise is a challenging problem. This paper proposes a detector based on a decreasing exponential function (DEF). The DEF detector can effectively suppress the impulsive noise and achieve good performance in the presence of $S{\alpha}S$ noise. The analytical expressions of the detection and false alarm probabilities of the DEF detector are derived, and the parameter optimization for the detector is discussed. A performance analysis shows that the DEF detector has much lower computational complexity than the Gaussian kernelized energy detector (GKED), and it performs better than the latter in $S{\alpha}S$ noise with small characteristic exponent values. In addition, the DEF detector outperforms the fractional lower order moment (FLOM)-based detector in $S{\alpha}S$ noise for most characteristic exponent values with the same order of magnitude of computational complexity.

• Journal of the Korea Society for Simulation
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• v.24 no.3
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• pp.89-96
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• 2015

In order to use missiles more effectively, assessing methodologies was advanced about weapon effects for various target types. We tried to find out the most effective analysis methodologies for missiles to attack 3 dimensional building target's and analyzed adaptedness as an assessing methodology. There are EFD (Expected Fractional Damage) and SSPD (Single Sortie Probability of Damage) methodologies to assess building target damage. In order to calculate effectiveness we used input parameter such as size of the target and CEP (Circular Error Probable), MAE_bldg (Mean Area of Effects for Building) of weapons and impact angle as encountering condition between the target and the missile. We compared EFD and SSPD, in order to analyze adaptedness as a effective methodology by CEP and MAE. The result was that EFD methodology was more adaptive to assess 3 dimensional building targets by missile systems than SSPD.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.173-182
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• 2014

The mixed convolved action principle provides a new rigorous weak variational formalism for a broad range of initial boundary value problems in mathematical physics and mechanics in terms of mixed formulation, convolution, and fractional calculus. In this paper, its potential in the development of numerical methods for transient problems in various dynamical systems when adopting temporally second order approximation is investigated. For this, the classical single-degree-of-freedom linear elastic dynamical systems are primarily considered to investigate computational characteristics of the developed algorithms. For the undamped system, all the developed algorithms are symplectic with respect to the time step. For the damped system, they are shown to be accurate with good convergence characteristics.

• Journal of the Ergonomics Society of Korea
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• v.28 no.4
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• pp.1-7
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• 2009

The purpose of this study was to evaluate the legibility of one-syllable Korean characters with the participation of sixteen subjects. The experiment considered nine factors including age (young and old), gender (male and female), illuminance (150lx and 600lx), viewing distance (50cm and 200cm), material type (paper and LCD), typeface (Ming and Gothic), thickness (plain and bold), color contrast (black letter/white background and white letter/black background), and complexity (simple, complex, and number) to examine main effects with a $2^{6-3}\times3$ fractional factorial design. The dependent variables were minimum character size of 100% correctness, maximum character size of 0% correctness, and minimum character size of comfortable reading preference. The results of analysis of variance (ANOVA) revealed that age, illuminance, viewing distance and complexity were significant for all dependent variables, except gender which was significant only for the minimum character size of comfortable reading preference. In general, the young could see twofold smaller size letters than the elderly. The subjects could see smaller sized letters with the illuminance of 600lx and viewing distance of 50cm than 150lx and 200cm, respectively and also with numbers, simple characters, and complex characters in that order. The findings of this study could be characterized about the legibility of Korean characters and be good resources for developing its standard.

• Journal of Power System Engineering
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• v.17 no.3
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• pp.72-81
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• 2013

Many articles have been published about a 2-degree of freedom model that includes the lateral and yaw motions for controller synthesis in intelligent transport system applications. In this paper, a 3-degree of freedom linear model that includes the roll motion is developed to design a robust steering controller for lane following maneuvers using ${\mu}$-synthesis. This linear perturbed system includes a set of parametric uncertainties in cornering stiffness and unmodelled dynamics in steering actuators. The state-space model with parametric uncertainties is represented in linear fractional transformation form. Design purpose can be obtained by properly choosing the frequency dependent weighting functions. The objective of this study is to keep the tracking error and steering input energy small in the presence of variations of the cornering stiffness coefficients. Furthermore, good ride quality has to be achieved against these uncertainties. Frequency-domain analyses and time-domain numerical simulations are carried out in order to evaluate these performance specifications of a given vehicle system. Finally, the simulation results indicate that the proposed robust controller achieves good performance over a wide range of uncertainty for the given maneuvers.