• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1540-1551
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• 2015

The detection of position and speed in BLDC motors without using position sensors has meant many efforts for the last decades. The aim of this paper is to develop a sensorless technique for detecting the position and speed of BLDC motors, and to overcome the drawbacks of position sensor-based methods by improving the performance of traditional approaches oriented to motor phase voltage sensing. The position and speed information is obtained by computing the derivative of the terminal phase voltages regarding to a virtual neutral point. For starting-up the motor and implementing the algorithms of the detection technique, a FPGA board with a real-time processor is used. Also, a versatile hardware has been developed for driving BLDC motors through pulse width modulation (PWM) signals. Delta and wye winding motors have been considered for evaluating the performance of the designed hardware and software, and tests with and without load are performed. Experimental results for validating the detection technique were attained in the range 5-1500 rpm and 5-150 rpm under no-load and full-load conditions, respectively. Specifically, speed and position square errors lower than 3 rpm and between 10º-30º were obtained without load. In addition, the speed and position errors after full-load tests were around 1 rpm and between 10º-15º, respectively. These results provide the evidence that the developed technique allows to detect the position and speed of BLDC motors with low accuracy errors at starting-up and over a wide speed range, and reduce the influence of noise in position sensing, which suggest that it can be satisfactorily used as a reliable alternative to position sensors in precision applications.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1273-1283
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• 2011

A 3-dimensional unsteady numerical analysis has been performed to evaluate the aerodynamic characteristics of a Giromill. Generally, the structure of a Giromill is simple and therefore easy to develop. In addition, the high solidity of the Gironmill helps improve the self-starting capacity at a low tip speed ratio (TSR). However, contrary to the Darrieus wind turbine which has a TSR of 4-7, a Giromill has a low TSR of 1-3. In this study, the aerodynamic characteristics of the Giromill are investigated using computational fluid dynamics (CFD). Three straight-bladed wings are used, and the solidity of the Giromill is 0.75. In contrast to a Darrieus wind turbine having low solidity, the Giromill shows a sudden decrease in the aerodynamic performance because of the interference between the wings and an increase in the drag on the wings in the downstream direction where wind flow is significantly reduced. Consequently, the aerodynamic performance decreased at a TSR value lower than 2.4.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.9
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• pp.563-570
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• 2017

Experimental and numerical studies were performed to investigate the performance and internal flow characteristics of a supersonic second throat exhaust diffuser (STED) with back pressure ($P_a$). An ejector system was used to vary the back pressure ($P_a$) conditions. The operating gas for the STED and the ejector was high pressure nitrogen at room temperature. When the back pressure ($P_a$) at a constant nozzle inlet pressure $P_0$) decreases, the pressure recovery location moves downstream. If the pressure ratio $P_0/P_a$) is the same, even if the nozzle inlet pressures $P_0$) are different, the diffuser's internal flow pattern and starting pressure ratio ($(P_0/P_a)_{st}$) are almost the same.

• Journal of the Korean Data and Information Science Society
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• v.28 no.2
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• pp.317-326
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• 2017

In this paper, we investigate the effects of performance and non-performance variables attributed to Korean professional baseball pitchers on annual salary by the records about pitchers between 2010 and 2016. We select the variables in reference to previous research related to this topic. The models are then estimated using linear regression model. For pitchers, age, experience in the league, year, eligibility for free agency, the number of wins, WAR, the number of innings pitched, the number of games, the number of saves, the number of games started, and type of baseball team have a statistically significant effect. Among the notable factors, affecting pitchers salaries are largely measure of starting pitchers. Pitcher sabermetrics indexes were poorly reflected on annual salary. The model presented here can be used to remove any unobjective salary differences for Korean professional baseball pitchers.

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.8
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• pp.445-452
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• 2004

Zoning technology of disk improved the performance of disk subsystem with increase of storage capacity and average transfer bandwidth. SCAN disk scheduling with double buffering is used to utilize the performance of zoned disk in multimedia system. However, this method has a problem that generates jitter when the number of steams increases. In this article, we propose the novel approach, pre-buffering policy, to overcome this problem. Pre-buffering avoids jitter by buffering the lack of data before starting service, which is estimated from the current cycle length and the maximum cycle length. We can calculate cycle length, data sire needed in each cycle and the possible lack of data caused by the increase of the number of streams using the numerical model of disk subsystem. Pre-buffering can be applied for multimedia systems and contribute to provide clients with high quality service without jitter.

• Journal of the Korean Ceramic Society
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• v.40 no.6
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• pp.507-512
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• 2003

The LiN $i_{l-y}$ $Co_{y}$ $O_2$ samples were synthesized at 80$0^{\circ}C$ and 85$0^{\circ}C$, by the solid-state reaction method, from the various starting materials LiOH, L $i_2$C $O_3$, NiO, NiC $O_3$, $Co_3$ $O_4$, CoC $O_3$, and their electrochemical properties are investigated. The LiN $i_{l-y}$ $Co_{y}$ $O_2$ pre-pared from L $i_2$C $O_3$, NiO, and $Co_3$ $O_4$ exhibited the $\alpha$-NaFe $O_2$ structure of the rhombohedral system (space group; R3m). As the Co content increased, the lattice parameters a and c decreased. The reason is that the radius of Co ion is smaller than that of Ni ion. The increase in da shows that two-dimensional structure develops better as the Co content increases. The LiN $i_{0.7}$ $Co_{03}$. $O_2$［HOO(800,0.3)] synthesized at 80$0^{\circ}C$from LiOH, NiO, and $Co_3$ $O_4$ exhibited the largest first discharge capacity 162 mAh/g. The size of particles increases roughly as the valve of y increases. The samples with the larger particles have the larger first discharge capacities. The cycling performances of the samples with the first discharge capacity larger than 150 mAh/g were investigated. The LiN $i_{0.9}$ $Co_{0.1}$ $O_2$［COO(850,0.1)］ synthesized at 85$0^{\circ}C$ from L $i_2$C $O_3$, NiO, and $Co_3$ $O_4$ showed an excellent cycling performance. The sample with the larger first discharge capacity will be under the more severe lattice destruction, due to the expansion and contraction of the lattice during intercalation and deintercalation, than the sample with the smaller first discharge capacity. As the first discharge capacity increases, the capacity fading rate thus increases.increases.s.s.s.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3317-3322
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• 2007

THC(Total Hydrocarbon) emissions during cold start and warm-up phase constitute the majority of THC emissions during the FTP-75 mode. As the basic approach to improve the emission performance of Gasoline engine during transient phase, the effect of spark timing retard from MBT on THC emission characteristics is studied by engine test using a Fast response Flame Ionization Detector(FFID). A cyclic analysis of the combustion process shows that high THC emissions are produced first few cycles during the transient phase. This paper presents the results of engine performance and emission of Gasoline engine with various spark timing. consequently, This paper was focused on the combustion phenomena with various spark timing during transient phase which was analyzed by Fast response Flame Ionization Detector (FFID) equipment to measure the cyclic THC emission characteristics.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.308-317
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• 2012

Reactive processing, such as reactive hot pressing (RHP) and reactive spark plasma sintering (R-SPS), is effective densification method to prepare $ZrB_2$-based ultra high temperature ceramics (UHTCs). The present paper reviewed some typical reactive processing of $ZrB_2$-based UHTCs. All the reactions from the starting materials in the reactive processing are thermodynamically favorable, which generate enough energy and driving force for the densification of the final products under a relatively low temperature. Besides, compared with non-reactive processing, anisotropic $ZrB_2$ grains, such as $ZrB_2$ platelets, can only be obtained in the reactive processing, resulting in an improvement of the mechanical properties.

• Earthquakes and Structures
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• v.3 no.2
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• pp.181-201
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• 2012

The benchmark on the ASCE cable-stayed bridge has gathered since its proposal the interest of many specialists in the field of the structural control and the dynamic response of long span bridges. Starting from the original benchmark statement in the MATLAB framework, a refined version of the bridge model is developed in the ANSYS commercial finite element environment. A passive structural control system is studied through non linear numerical analyses carried out in time domain for several seismic realizations in a multiple support framework. An innovative electro-inductive device is considered. Its positive performance is compared with an alternative version considering traditional metallic dampers.

• Advances in aircraft and spacecraft science
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• v.3 no.4
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• pp.503-521
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• 2016

Variances in turbomachinery blades caused by manufacturing, operation or regeneration can result in modified structural behavior. In this work, the scatter of geometrical and material properties of a turbine blade and its influence on structure performance is discussed. In particular, the vibration characteristics and the lifetime of a turbine blade are evaluated. Geometrical variances of the surface of the blades are described using the principal component analysis. The scatter in material properties is considered by 16 varying material parameters. Maximum vibration amplitudes and the number of load cycles the turbine blade can withstand are analyzed by finite element simulations incorporating probabilistic principles. The probabilistic simulations demonstrate that both geometrical and material variances have a significant influence on the scatter of vibration amplitude and lifetime. Dependencies are quantified and correlations between varied input parameters and the structural performance of the blade are detected.