• Journal of Power Electronics
• /
• v.16 no.2
• /
• pp.399-413
• /
• 2016

This paper presents a topology for a modular power electronic transformer (PET) and a control scheme. The proposed PET consists of a cascaded H-Bridge rectifier on the primary side, a high-frequency DC/DC conversion cell in the center, and a cascaded H-Bridge inverter on the secondary side. It is practical to use PETs in power systems to reduce the cost, weight and size. A detailed analysis of the structure is carried out by using equivalent circuit. An algorithm to control the voltages of each capacitor and to maintain the power flow in the PET is established. The merits are analyzed and verified in theory, including the bi-directional power flow, variable voltage/frequency and high power factor on the primary side. The experimental results validated the propose structure and algorithm.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.10a
• /
• pp.754-759
• /
• 2008

Recently, the construction of buildings and large bridges has been increasing rapidly causing foundation structure growing larger then before, especially in the use of large size cast-in-place piles. Barrette Pile will usually be used at the site where diaphragm wall is the retaining wall to save time and cost in mobilization of equipments. This study uses bi-directional loading test data obtained from two different sites to observe the bearing capacity and displacement characteristics of barrette pile. Numerical analysis of the test is done by using commercial 3D computer program and the interface effect and capacity of the pile as well as displacement characteristics of the pile is verified.

• Structural Engineering and Mechanics
• /
• v.27 no.1
• /
• pp.49-61
• /
• 2007

This paper presents a modified and improved bi-directional evolutionary structural optimization (BESO) method for topology optimization. A sensitivity filter which has been used in other optimization methods is introduced into BESO so that the design solutions become mesh-independent. To improve the convergence of the optimization process, the sensitivity number considers its historical information. Numerical examples show the effectiveness of the modified BESO method in obtaining convergent and mesh-independent solutions. A study of the effects of various BESO parameters on the solution is then conducted to determine the appropriate values for these parameters.

• Journal of Korea Society of Digital Industry and Information Management
• /
• v.10 no.4
• /
• pp.133-142
• /
• 2014

The least mean square(LMS) algorithm has been popular owing to its simplicity, stability, and availability to implement. But it inherently has a problem of slow convergence speed, and the presence of a transfer function in the secondary path following the adaptive controller and the error path has been shown to generally degrade the stability and the performance of the LMS algorithm in applications of acoustical noise control. In general, in order to solve these problems, the filtered-x LMS (FX-LMS) type algorithms can be used and the bi-directional Filtered-x LMS(BFXLMS) algorithm is very attractive among them, which increase the convergence speed and the performance of the controller with nearly equivalent computation complexity. In this paper, a mathematical analysis for the BFXLMS algorithm is presented. In terms of view points of time domain, frequency domain, and stochastic domain, the characteristics and stabilities of algorithm is accurately analyzed.

• Structural Engineering and Mechanics
• /
• v.85 no.1
• /
• pp.135-145
• /
• 2023

This study presents the free vibrational responses of bi-directional axially graded cylindrical shell panels using 3D graded finite element approximation under a temperature field. The cylindrical shell panel is graded in two directions and made of metal-ceramic materials. To extract material properties, the Voigt model is combined with a Power-law material distribution. Convergence and validation studies are performed on the developed computational model to ensure its accuracy and effectiveness. Furthermore, a parametric study is performed to evaluate the developed model, which demonstrates that geometrical parameters, imperfect materials (porosity), support conditions, and surface temperature all have a significant impact on the free vibration responses of a bi-directional axially graded cylindrical shell panel in a thermal environment.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.28 no.10
• /
• pp.16-26
• /
• 2014

This paper proposes new 13-level inverter topology and DC/DC converter buck-boost structure topology for multilevel, compounding uni-directional and bi-directional switches, and proposes high-efficient multilevel inverter system in which the proposed two PCS(Power Conditioning System) was connected in series. In proposed multilevel inverter of forming a output 13-level phase voltage by using total 18 switching parts, Then bi-directional switch has a characteristic of reducing conduction loss and controlling the reactive power effectively by separating electrically from the neutral point. DC/DC converter for supplying in dependent 3 DC voltage to the proposed multi-level inverter generates 180-degree phase shifted PWM by the symmetrically combined structure of 2 buck-boost converter and twice switching frequency efficiency can be obtained, meanwhile, the converter can step up/down the output voltage and 20% output can be generated comparing the input voltage. This proposed system is verified with the simulation and laboratory test.

• Earthquakes and Structures
• /
• v.10 no.3
• /
• pp.563-588
• /
• 2016

In this study, solution models are proposed to obtain code-compatible ground motion record sets which can be used for both uni-directional and bi-directional dynamic analyses. Besides scaled, unscaled ground motion record sets are obtained to show the utility and efficiency of the solution models. For scaled ground motion sets the proposed model is based on hybrid HS-Solver which integrates heuristic harmony search (HS) algorithm with the spreadsheet Solver add-in. For unscaled ground motion sets HS based solution model is proposed. Design spectra defined in Eurocode-8 for different soil types are selected as target spectra. The European Strong Motion Database is used to get ground motion record sets. Also, a sensitivity analysis is conducted to evaluate the effect of different HS solution parameters on the solution accuracy. Results show that the proposed solution models can be regarded as efficient ways to develop scaled and unscaled ground motion sets compatible with code-based design spectra.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.37 no.2B
• /
• pp.97-109
• /
• 2012

In this paper, we propose a modulation scheme for a network-coded bi-directional relaying (NBR) system over an asymmetric channel, which means that the qualities of the relay channel (the link between the BS and RS) and access channel (the link between the RS and MS) are not identical. The proposed scheme employs a dual constellation in such a way that the RS broadcasts the network-coded symbols modulated by two different constellations to the MS and BS over two consecutive transmission intervals. We derive an upper bound on the average bit error rate (BER) of the proposed scheme, and compare it with the hybrid constellation-based modulation scheme proposed for the asymmetric bi-directional link. Furthermore, we investigate the channel utilization of the existing bi-directional relaying schemes as well as the NBR system with the proposed dual constellation diversity-based modulation (DCD). From our simulation results, we show that the DCD gives better average BER performance about 3.5~4dB when $E_b/N_0$ is equal to $10^{-2}$, while maintaining the same spectral efficiency as the existing NBR schemes over the asymmetric bi-directional relaying channel.

• Journal of the Korean Geosynthetics Society
• /
• v.13 no.4
• /
• pp.77-85
• /
• 2014

The helical pile has become popular with some constructional advantages because relatively compact equipment is needed for installing helical piles. However, field loading tests for estimating the bearing capacity of helical piles have drawbacks that the required dead load should be as much as the operation load, and reaction piles or anchors are required. In this paper, the bi-directional load test without necessity of reaction piles and loading frames was applied to the helical pile, and the load-settlement curves of the helical piles were measured. The bi-directional load test was performed in two separate stages with the aid of a special hydraulic cylinder whose diameter is equal to that of the pile shaft. In the first stage, the hydraulic cylinder is assembled immediately above the bottom helix plate, and the end bearing capacity of the helical pile is measured. In the second stage, the hydraulic cylinder is assembled above the top helix plate, and the skin friction of the helical pile is measured. The pile loading-test program was carried out for the two different helical piles with the shaft diameter of 89 mm and 114 mm, respectively. However, the configuration of helix plates is identical with three helix plates of 450-, 350-, 200- mm diameter. Results of the bi-directional load test were verified by the conventional static pile loading test. As a result, the bearing capacity estimated by the bi-directional load test is in good agreement with the result of the conventional pile loading test.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.13 no.3
• /
• pp.254-258
• /
• 2000

Current leads of high $T_{c}$ superconductor were fabricated with Bi excess B $i_{2.2}$/S $r_{1.8}$/C $a_{1}$/C $u_{2}$/ $O_{x}$ composition by rapid cooling method. The dimensions of final samples were fixed 3 mm and 8 mm diameter with 50 mm length each To control uniform density the samples were preformed by CIP(Cold Isostatic Press) process and followed by partial or full melting process after raising up to 90$0^{\circ}C$ for 30min. Plate shaped microstructure was clearly observed adjacent to the Ag tube wall and the size of plate was about 100$\mu$m. However the severe destruction of growth orientation was shown in the inner growth part. critical temperature ( $T_{c}$) was about 53~71K after directional growth while Tc was decreased about 77~80 K before directional growth. After directional growth critical current( $I_{c}$) and critical current density( $J_{c}$) in the specimen of 8 mm diameter at 50 K were about 110 A and 280 A/c $m^2$ respectively.pectively.ely.