• Journal of Korean Society of Steel Construction
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• v.19 no.1
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• pp.107-115
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• 2007

In this paper, the damping ratios of two methods, namely the half-power bandwidth method and random decrement method from the vibration measurement were examined. Ambient vibration tests were conducted on two steel-framed and one composite tall building ranging from 27 to 36 stories. The performance of the half-power bandwidth method was investigated using four sample sizes, such as 1024, 2048, 4096 and 8192. Damping by the half-power bandwidth method is slightly more overestimated than the random decrement method due to insufficient record length. Damping evaluation by the half-power bandwidth method was found to be enhanced when using the narrower bandwidth with long recorded data.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.533-540
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• 2001

Material damping is an important parameter to evaluate the site response by a dynamic loading. Currently the material damping of the subgrade is mainly determined by a resonant column testing. Typical methods to evaluate material damping include half-power bandwidth method and free-vibration decay method. In the large strain range, the half-power bandwidth method gives an erratic damping factor, because the method is based on the assumption of the linear behavior of a specimen. The free-vibration decay method has also limitations in that the damping factors vary with the range of cycles in calculation, and also in that the specific shear strain can not be designated for the free vibration. In this study, the frequency-phase method, which was developed to evaluate material damping of a beam simply supported, is introduced to evaluate the material damping by the resonant column testing. Also, the comparison among half-power method, free-vibration decay method and the frequency-phase method is provided for a remolded sand.

• Journal of Korean Association for Spatial Structures
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• v.8 no.2
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• pp.95-103
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• 2008

This paper is concerned with the damping ratios of two methods, which are frequency domain and time domain approach. Ambient vibrations and synchronized human excitation test were conducted to three reinforced concrete buildings ranging from eleven to nineteen stories. The performance of the half power bandwidth method was investigated using three kinds of sample size, 1024, 2048, and 4096. The damping ratio by synchronized human excitation ranges from 1.05% to 1.22% in the long direction and from 1.16% to 1.50% in short direction. Damping by half power bandwidth method is slightly more overestimated than the synchronized human excitation due to insufficient record length. Damping evaluation by half power bandwidth method was found to be enhanced by using the narrower bandwidth with long recorded data.

• Nuclear Engineering and Technology
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• v.48 no.3
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• pp.673-683
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• 2016

This paper analyzes the accuracy of the methods used in calibrating the thermal power of Nigeria Research Reactor-1 (NIRR-1), a low-power miniature neutron source reactor located at the Centre for Energy Research and Training, Ahmadu Bello University, Zaria, Nigeria. The calibration was performed at three different power levels: low power (3.6 kW), half power (15 kW), and full power (30 kW). Two methods were used in the calibration, namely, slope and heat balance methods. The thermal power obtained by the heat balance method at low power, half power, and full power was $3.7{\pm}0.2kW$, $15.2{\pm}1.2kW$, and $30.7{\pm}2.5kW$, respectively. The thermal power obtained by the slope method at half power and full power was $15.8{\pm}0.7kW$ and $30.2{\pm}1.5kW$, respectively. It was observed that the slope method is more accurate with deviations of 4% and 5% for calibrations at half and full power, respectively, although the linear fit (slope method) on average temperature-rising rates during the thermal power calibration procedure at low power (3.6 kW) is not fitting. As such, the slope method of power calibration is not suitable at lower power for NIRR-1.

• Journal of the Semiconductor & Display Technology
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• v.6 no.2 s.19
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• pp.45-48
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• 2007

The proposed method offers an improved DC/DC converter scheme to increase power density. It is based on half-bridge topology with newly introduced pulse-grouping control method, which helps to reduce the transformer size and the volume of semiconductor devices maintaining high efficiency. Test results with 85W(18.5V/4.6A) design shows that the measured efficiency is 93.5% with power density of $36W/in^3$.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.1
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• pp.56-64
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• 2006

Recently, high density power supply has been researched over the last few years. To achieve high density power supply, the series resonant converter has been steadily used. In this paper, the half-bridge series resonant converter using the integrated Inductor-Inductor-Capacitor-Transformer(LLCT) is described. The structure of LLCT is analysed by the use of Finite Element Method Magnetics(FEMM) Software. Also the experimental results are verified by the simulation based on the theoretical analysis and the 300W experimental prototype.

• The Transactions of the Korean Institute of Power Electronics
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• v.2 no.3
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• pp.26-36
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• 1997

An single stage AC/DC converter based on half bridge topology suitable for low power level applications is proposed. The proposed converter has high power factor, low harmonic distortion, and tight output regulations. Asymmetrical control and synchronous rectification are adopted to reduce the switching loss and rectification loss, respectively. The modelling employing average modelling method and detailed analysis are performed to derive the design equations. According to these design equations, a prototype converter has been designed and experimented. This prototype meets the IEC 555-2 regulations with near unity power factor and high efficiency.

• Journal of KSNVE
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• v.9 no.6
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• pp.1187-1192
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• 1999

The purpose of this study is to determine the most appropriate experimental method of the measurement of "damping loss factors" (DLF) for the statistical energy analysis(SEA) calculation. The successful prediction of vibration levels from the structure is critically dependent on the accurate estimation of DLF's not only in conventional vibration analysis but especially in SEA. Unforunately, calculation of accurate DLF is not an easy matter. So experimental methods are made use of for the DLF values. Three kinds of experimental methods for estimating DLF, i.e. decay rate method, half-power bandwidth method and power balance method, are presented and tests are carried out for the plate and the cylindrical shell examples. Pro and con of each methods is reviewed. Finally, calculated DLF values are used for vibration level estimation using commercial SEA software and compared with measured vibration data.tion data.

• JSTS:Journal of Semiconductor Technology and Science
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• v.1 no.3
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• pp.167-181
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• 2001

A stepwise driving method was used for reducing the AC power consumption in a TFT-LCD. The AC power takes the largest portion of the total power consumption of a TFT-LCD. Experimental results confirmed that the AC power saving efficiency reached up to 75% when a 5-stepwise driving with each step time of $2\mu$ sec was applied to a 14.1 inch-diagonal XGA TFT-LCD. The second largest component of power consumption called the DC power comes from the quiescent currents in Op-amps. A simple and efficient architecture was proposed in this work to reduce this DC power consumption: Half of the Op-amps have the 5V-supplies, and the rest half have the 10V-supplies, and two Op-amps are shared by adjacent two channels. Measurements of test circuits showed that this simple method could reduce over 40% of the DC power consumption..

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.85-89
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• 1998

A switching power stage is a very nonlinear system because it has two or more operation modes in one switching cycle. To model a switching power stage, the state space averaging method has been developed. Though it allows a unified treatment of a large variety of switching power stages, the model it yields is always very nonlinear. So, it is required to linearize the averaged model. But it is well known that a controller for a nonlinear plant designed by the linearization frequently fails in showing satisfactory control performance. Hence it is very natural to try to design a nonlinear controller for a switching power stage. In design of a switching power system, nonlinear control approaches such as adaptive control and fuzzy control have been widely studied so far. In this research, a recently developed control method, time delay control is briefly studied and a design example for a ZVS PWM half bridge converter is given. The performance of the time delay controller is compared to its conventional counterpart, PI controller by computer simulations.