• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.9
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• pp.1337-1346
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• 2015

In this paper, pattern classifier is designed to classify precipitation and non-precipitation events from weather radar data. The proposed classifier is based on Fuzzy Neural Network(FNN) and consists of three FNNs which operate in parallel. In the proposed network, the connection weights of the consequent part of fuzzy rules are expressed as two polynomial types such as constant or linear polynomial function, and their coefficients are learned by using Least Square Estimation(LSE). In addition, parametric as well as structural factors of the proposed classifier are optimized through Differential Evolution(DE) algorithm. After event classification between precipitation and non-precipitation echo, non-precipitation event is to get rid of all echo, while precipitation event including non-precipitation echo is to get rid of non-precipitation echo by classifier that is also based on Fuzzy Neural Network. Weather radar data obtained from meteorological office is to analysis and discuss performance of the proposed event and echo patter classifier, result of echo pattern classifier compare to QC(Quality Control) data obtained from meteorological office.

• Advanced Composite Materials
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• v.16 no.1
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• pp.1-10
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• 2007

Composite materials consisting of crushed carbon fiber reinforced plastics (CFRP) pieces and acrylonitrile-butadiene-styrene (ABS) resin were prepared by an injection mold method to solve the problem of recycling of CFRP. The electrical properties, such as electrical resistivity, alternating current impedance and electromagnetic interference (EMI) shielding effect, were measured for the composites. The electrical resistivity of the composites showed a percolation type of conduction behavior and no difference between parallel and perpendicular to the injection direction was observed for CFRP content higher than the critical value. Measurement of alternating current impedance revealed that the conduction mechanism is attributed to the direct conductive paths generated by distributed carbon fibers; however, strong frequency dependence of the impedance was observed for the CFRP content near the critical one. The frequency dependence of the impedance is caused by the inter-fiber connection and can be expressed as a simple equivalent circuit. The absorption component of shielding effect (SE) was smaller than the expected value estimated from its resistivity. The decline of SE is thought to be caused by the decrease in effective thickness due to fiber orientation.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1741-1749
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• 2001

Recent studies of the structure of wall turbulence have lead to the development of a conceptual model that validates and integrates many elements of previous models into a relatively simple picture based on self-assembling packets of hairpin vortex eddies. By continual spawning new hairpins the packets grow longer in the streamwise direction, and by mutual induction between adjacent hairpins the hairpins are strained so that they grow taller and wider as they age. The result is a characteristic growth angle in the streamwise-wall normal plane. The spanwise growth of individual packets implies that packets must either merge or pass through each other when they come into contact. Direct numerical simulations of the growth and interaction of spanwise adjacent hairpins shows that they merge by the vortex connection mechanism originally proposed by Wark and Nagib (199). In this mechanism the quasi-streamwise legs of two hairpins annihilate each other, by virtue of having opposite vorticity, leaving a new hairpin of approximately double the width of the individuals. PIV measurements in planes parallel to the wall support this picture. DNS of multiple hairpins shows how the spanwise scale doubles when the hairpins form an array.

• Structural Engineering and Mechanics
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• v.17 no.2
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• pp.187-201
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• 2004

A shaking table test on a three-story one-bay steel frame model with metallic yield dampers and their parallel connection with oil dampers is carried out to study the dynamic characteristics and seismic performance of the energy dissipation system. It is found from the test that the combined energy dissipation system has favorable reducing vibration effects on structural displacement, and the structural peak acceleration can not evidently be reduced under small intensity seismic excitations, but in most cases the vibration reduction effect is very good under large intensity seismic excitations. Test results also show that stiffness of the energy dissipation devices should match their damping. Dynamic analysis method and mechanics models of these two dampers are proposed. In the analysis method, the force-displacement relationship of the metallic yield damper is represented by an elastic perfectly plastic model, and the behavior of the oil damper is simulated by a velocity and displacement relative model in which the contributions of the oil damper to the damping force and stiffness of the system are considered. Validity of the analytical model and the method is verified through comparison between the results of the shaking table test and numerical analysis.

• Structural Engineering and Mechanics
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• v.57 no.6
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• pp.1051-1064
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• 2016

Link-to-column connections in Eccentrically Braced Frames (EBFs) have critical role in their safety and seismic performance. Accordingly, in this study, contribution of supplemental stiffeners on hysteretic behavior of the link-to-column connection is investigated. Considered stiffeners are placed on both sides and parallel to the link web between the column face and the first stiffener of the link. Hysteretic behaviors of the link beams with supplemental stiffeners are numerically investigated using a pre-validated numerical model in ANSYS. It turned out that supplemental stiffeners can change energy dissipation mechanism of intermediate links from shear-flexure to shear. Both rectangular and trapezoidal supplemental stiffeners are studied. Moreover, optimal placement of the supplemental stiffeners is also investigated. Obtained results indicate a discrepancy of less than 9% in maximum link shear of the numerical and experimental specimens. This indicates that the numerical results are in good agreement with those obtained from the test. Trapezoidal supplemental stiffeners improve rotational capacity of the link. Moreover, use of two supplemental stiffeners at both ends of the link can more effectively improve hysteretic behavior of intermediate links. Supplemental stiffeners would also alleviate the imposed demands on the connections. This latter feature is more pronounced in the case of two supplemental stiffeners at both ends of the link.

• JSTS:Journal of Semiconductor Technology and Science
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• v.3 no.3
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• pp.145-152
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• 2003

Electrical gate and drain characteristics of double heterostructure InAlAs/InGaAs pseudomorphic HEMTs have been investigated under sub-bandgap photonic excitation ($hv). Drain $(V_{DS})-,{\;}gate($V_{DS})-$, and optical power($P_{opt}$)-dependent variation of the abnormal gate leakage current and associated physical mechanisms in the PHEMTs have been characterized. Peak gate voltage ($V_{GS,P}$) and the onset voltage for the impact ionization ($V_{GS.II}$) have been extracted and empirical model for their dependence on the $V_{DS}$ and $P_{opt} have been proposed. Anomalous gate and drain current, both under dark and under sub-bandgap photonic excitation, have been modeled as a parallel connection of high performance PHEMT with a poor satellite FET as a parasitic channel. Sub-bandgap photonic characterization, as a function of the optical power with $h\nu=0.799eV$, has been comparatively combined with those under dark condition for characterizing the bell-shaped negative humps in the gate current and subthreshold drain leakage under a large drain bias.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.100-106
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• 2009

A novel 8 V DC power source with an external series-parallel connection of 50 Dye-sensitized Solar Cells (DSCs) has been proposed. One DSC has the optimized length to width ratio of $5.2{\times}2.6\;cm$ and an active area $8\;cm^2$ ($4.62{\times}1.73\;cm$) which attained a conversion efficiency of 4.02%. From the electrochemical impedance spectroscopic analysis, it was found that the resistance elements related to the Pt electrode and electrolyte interface behave like that of diode and the series resistance corresponds to the sum of the other resistance elements. Surface morphology and sheet resistance of Pt counter electrode did not degrade the performance of the cell. This novel 8V-0.33A DC power source shows stable performance with an energy conversion efficiency of 4.24% under 1 sun illumination (AM 1.5, Pin of $100\;mW/cm^2$).

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.2210-2211
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• 2008

In this paper, we investigated the quenching characteristics of a superconducting fault current limiter (SFCL) with connection of $2{\times}3$ matrixes. This SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit the fault current. When the fault occurs, the magnetic field generated in the reactor connected in parallel was applied to the two superconducting units of the current-limiting part to reduce of inhomogeneous critical current behavior between the superconducting units. The quenching behavior of a superconducting unit in the trigger part was affected by the increase of turn numbers. This is because of the difference of current distribution between the inductance of the reactors and the resistance generated in the superconducting units in trigger part. We confirmed that the voltage differences between two superconducting units of the current-limiting part were decreased. This is because of the improvement of inhomogeneous critical current behavior between the superconducting units according to the increase of external magnetic field.

• Smart Structures and Systems
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• v.13 no.4
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• pp.567-585
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• 2014

The piezoelectric transverse $d_{15}$ shear sensing mechanism is firstly assessed experimentally for a cantilever smart sandwich plate made of a piezoceramic axially poled patched core and glass fiber reinforced polymer composite faces. Different electrical connections are tested for the assessment of the sensor performance under a varying amplitude harmonic (at 24 Hz) force. Also, the dynamic response of the smart sandwich composite structure is monitored using different acquisition devices. The obtained experimentally sensed voltages are compared to those resulting from the benchmark three-dimensional piezoelectric coupled finite element simulations using a commercial code where realistic features, like equipotential conditions on the patches' electrodes and mechanical updating of the clamp, are considered. Numerically, it is found that the stiffness of the clamp, which is much softer than the ideal one, has an enormous influence on the sensed voltage of its adjacent patch; therefore, sensing with the patch on the free side would be more advantageous for a cantilever configuration. Apart from confirming the latter result, the plate benchmark experimental assessment showed that the parallel connection of its two oppositely poled patches has a moderate performance but better than the clamp side patch acting as an individual sensor.

• Journal of Electrical Engineering and Technology
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• v.6 no.3
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• pp.293-301
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• 2011

This paper presents a novel theoretical method based on power analysis to obtain voltage reference values for an inverter-based compensator. This type of compensator, which is installed in parallel with the load, is usually referred to as the active filter. The proposed method is tailored to design the compensator in such a way that it can simultaneously balance the asymmetric load, as well as correct the power factor of the supply side. For clarity, a static compensator is first considered and a recursive algorithm is utilized to calculate the reactance values. The algorithm is then extended to calculate voltage reference values when the compensator is inverter based. It is evident that the compensator would be asymmetric since the load is unbalanced. The salient feature associated with the proposed method is that the circuit representation of system load is not required and that the load is recognized just by its active and reactive consumptions. Hence, the type and connection of load do not matter. The validity and performance of the new approach are analyzed via a numerical example, and the obtained results are thoroughly discussed.