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- 저자 : Lee. JiHo (검색결과 812 건)
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Effect of beam slope on the static aerodynamic response of edge-girder bridge-deck
Lee, Hoyeop,Moon, Jiho,Chun, Nakhyun,Lee, Hak-eun Techno-Press 2017 Wind and Structures, An International Journal (WAS Vol.25 No.2
2-edge box girder bridges have been widely used in civil engineering practice. However, these bridges show weakness in aerodynamic stability. To overcome this weakness, additional attachments, such as fairing and flap, are usually used. These additional attachments can increase the cost and decrease the constructability. Some previous researchers suggested an aerodynamically stabilized 2-edge box girder section, giving a slope to the edge box instead of installing additional attachments. However, their studies are limited to only dynamic stability, even though static aerodynamic coefficients are as important as dynamic stability. In this study, focus was given to the evaluation of static aerodynamic response for a stabilized 2-edge box girder section. For this, the slopes of the edge box were varied from $0^{\circ}$ to $17^{\circ}$ and static coefficients were obtained through a series of wind tunnel tests. The results were then compared with those from computational fluid dynamics (CFD) analysis. From the results, it was found that the drag coefficients generally decreased with the increasing box slope angle, except for the specific box slope range. This range of box slope varied depending on the B/H ratio, and this should be avoided for the practical design of such a bridge, since it results in poor static aerodynamic response.
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Lee, Jiho,Kim, Jaeha The Institute of Electronics and Information Engin 2015 Journal of semiconductor technology and science Vol.15 No.5
In simulation-based circuit optimization, many simulation runs may be wasted while evaluating infeasible designs, i.e. the designs that do not meet the constraints. To avoid such a waste, this paper investigates the use of support vector machine (SVM) classifiers in predicting the design's feasibility prior to simulation and the optimal selection of the SVM parameters, namely, the Gaussian kernel shape parameter ${\gamma}$ and the misclassification penalty parameter C. These parameters affect the complexity as well as the accuracy of the model that SVM represents. For instance, the higher ${\gamma}$ is good for detailed modeling and the higher C is good for rejecting noise in the training set. However, our empirical study shows that a low ${\gamma}$ value is preferable due to the high spatial correlation among the circuit design candidates while C has negligible impacts due to the smooth and clean constraint boundaries of most circuit designs. The experimental results with an LC-tank oscillator example show that an optimal selection of these parameters can improve the prediction accuracy from 80 to 98% and model complexity by $10{\times}$.
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Jiho Lee,Sukjin Choi,Young Jin Hwang,Woo Seung Lee,Yeong-Chun Kim,Tae Kuk Ko IEEE 2012 IEEE transactions on applied superconductivity Vol.22 No.3
<P>There are a number of AC power devices using high temperature superconductor (HTS) such as Superconducting Fault Current Limiter (SFCL), Superconducting Transformer, AC Superconducting cable and so on. However, the operating current of HTS power devices at alternating current (AC) circumstances is almost decided by critical current which is measured in direct current (DC) circumstances. Applying DC critical current criterion to AC power devices cannot be ideal. So, for AC power devices, a new AC critical current criterion must be needed. Commercial AC frequencies of current grid are 50 and 60 Hz. Therefore, in AC circumstance, the voltage induced by inductance is not negligible. For this paper, AC conducting experiments on variable super conducting tape samples were executed. The voltage induced by inductance is removed by filtering process and the voltage produced by resistance remains and is considered as a parameter (or guide line) of quench. With filtering process, amplitude of voltage generated by resistance can be calculated. As a result of those experiments, the `Amplitude of input current'-`amplitude of voltage induced by resistance' curve was acquired and alternating critical current criteria were inferred.</P>
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Cytohistological study of the leaf structures of Panax ginseng Meyer and Panax quinquefolius L.
Lee, Ok Ran,Nguyen, Ngoc Quy,Lee, Kwang Ho,Kim, Young Chang,Seo, Jiho The Korean Society of Ginseng 2017 Journal of Ginseng Research Vol.41 No.4
Background: Both Panax ginseng Meyer and Panax quinquefolius are obligate shade-loving plants whose natural habitats are broadleaved forests of Eastern Asia and North America. Panax species are easily damaged by photoinhibition when they are exposed to high temperatures or insufficient shade. In this study, a cytohistological study of the leaf structures of two of the most well-known Panax species was performed to better understand the physiological processes that limit photosynthesis. Methods: Leaves of ginseng plants grown in soil and hydroponic culture were sectioned for analysis. Leaf structures of both Panax species were observed using a light microscope, scanning electron microscope, and transmission electron microscope. Results: The mesostructure of both P. ginseng and P. quinquefolius frequently had one layer of non-cylindrical palisade cells and three or four layers of spongy parenchymal cells. P. quinquefolius contained a similar number of stomata in the abaxial leaf surface but more tightly appressed enlarged grana stacks than P. ginseng contained. The adaxial surface of the epidermis in P. quinquefolius showed cuticle ridges with a pattern similar to that of P. ginseng. Conclusion: The anatomical leaf structure of both P. ginseng and P. quinquefolius shows that they are typical shade-loving sciophytes. Slight differences in chloroplast structure suggests that the two different species can be authenticated using transmission electron microscopy images, and light-resistant cultivar breeding can be performed via controlling photosynthesis efficiency.
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Lee, Woo Seung,Lee, Jiho,Song, Seunghyun,Park, Young Gun,Jin, Hongwoo,Hahn, Seungyong,Ahn, Min Cheol,Ko, Tae Kuk Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3
<P>A semipersistent current-mode operation with a high-temperature superconducting (HTS) coil is very useful for some applications, including maglev. An HTS coil for semipersistent mode operation includes at least one residual joint to make a closed-loop coil. A low current decaying rate is achieved by reducing the residual joint resistance. This paper suggests a winding method with a turn-to-turn soldering process. The turn-to-turn soldering process provides a wide flow path for the charged current in the HTS coil during the semipersistent mode operation. Therefore, the total equivalent residual resistance is reduced. However, this reduced residual resistance also prevents the current from participating in the charging process. Therefore, a new current charging method for the turn-to-turn soldered HTS coil needs to be tested. In this paper, a small-scale sample HTS coil with turn-to-turn soldering method is fabricated for testing. A simple charging–discharging experiment is performed on the sample coil. The time constant of the sample coil is calculated from the experimental results. A fast current charging sequence for the turn-to-turn soldered coil is also tested and analyzed from the perspective of power and energy consumption during the current charging operation.</P>
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Lee, Jiho,Kim, Wonbin,Kim, Woong American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.16
<P>A critical problem with stretchable supercapacitors developed to date has been evaporation of a volatile component of their electrolyte, causing failure. In this work, we demonstrated successful use of an ionic-liquid-based nonvolatile gel (ion–gel) electrolyte in carbon nanotube (CNT)-based stretchable supercapacitors. The CNT/ion–gel supercapacitors showed high capacitance retention (96.6%) over 3000 stretch cycles at 20% strain. The high durability against stretch cycles was achieved by introducing microroughness at the interfaces between different materials. The microroughness was produced by the simple process of imprinting the surface microstructure of office paper onto a poly(dimethylsiloxane) substrate; the surface texture is reproduced in successive current collector and CNT layers. Adhesion between the different layers was strengthened by this roughness and prevented delamination over repeated stretch cycles. The addition of a CNT layer decreased the sensitivity of electrical characteristics to stretching. Moreover, the ion–gel increases the operating voltage window (3 V) and hence the energy density. We believe our demonstration will greatly contribute to the development of flexible and/or stretchable energy-storage devices with high durability.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-16/am502953g/production/images/medium/am-2014-02953g_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am502953g'>ACS Electronic Supporting Info</A></P>
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Staggered swirler arrangement in two self-excited interacting swirl flames
Lee, Taesong,Lee, Jiho,Park, Junhyeong,Han, Dongsik,Kim, Kyu Tae Elsevier 2018 Combustion and flame Vol.198 No.-
<P><B>Abstract</B></P> <P>Interference of acoustic and convective disturbances controls the development of self-excited combustion oscillations of a lean-premixed swirl-stabilized flame with a central bluffbody. How this interference mechanism influences the dynamics of multiple interacting flames in a multi-nozzle environment is currently unknown. Here we present observations of a multi-nozzle system's response to staggered swirler arrangements (<I>ξ</I> <SUB>sw, 1</SUB> ≠ <I>ξ</I> <SUB>sw, 2</SUB>) as compared to non-staggered arrangements; the distance between the swirler and the flame is the dominant length scale of vortical disturbances. Our results demonstrate that a slight modification of the swirler arrangement in the streamwise direction – staggered or non-staggered – has a remarkable influence on the stability map of the whole combustion system. Phase-resolved flame imaging measurements indicate that under non-staggered conditions interacting swirl flames feature a coherent motion during a period of oscillation. By contrast, the staggered swirler combination creates significantly non-symmetric flame dynamics, disturbing the development of well-organized motion over the entire reaction zone. Flame surface modulations in the lateral direction are particularly pronounced due to the formation of non-symmetric convection delays of vortical disturbances between adjacent swirl nozzles. For a given swirler arrangement, the system's response to a wide range of combinations of mean nozzle velocities, including symmetric ( <SUB> u ¯ 1 </SUB> = <SUB> u ¯ 2 </SUB> ) and non-symmetric ( <SUB> u ¯ 1 </SUB> ≠ <SUB> u ¯ 2 </SUB> ) conditions, were explored to account for the simultaneous effects of the two convection parameters. Our data show that a major determinant of the onset of the instability is the combination of the Strouhal numbers, ⟨St<SUB>1</SUB>, St<SUB>2</SUB>⟩, which can be even or uneven depending on the manipulation of the convection time of each nozzle.</P>
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