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이진국,이동희,안진우 경성대학교 공학기술연구소 2005 공학기술연구지 Vol.12 No.-
This paper presents a development of Switched Reluctance Motor (SRM) drive system for a hoist application. In the hoist system, smoothing start-up and braking are very important for a protection of goods. In order to improved a start-up and a stop performance of hoist system, the smoothing operation sequence of SRM using direct instantaneous torque control is proposed. The proposed Direct Instantaneous Torque Control (DITC) the instantaneous torque of SRM according to the switching sequence and hysteric band. In order to compare the reference and actual torque of SRM, pre-measured flux and torque look-up table are regulate used. The proposed SRM Drive system is verified by the simulation result.
이동희,이진국,안진우 경성대학교 공학기술연구소 2005 공학기술연구지 Vol.12 No.-
This paper proposes high speed SRM drive system for blower with a novel 4-level inverter and precise excitation position generator. In order to get a fast build-up and a demagnetization of excitation current, 4-level inverter system is proposed. The proposed 4-level inverter has additional charge capacitor, power switch and diode in the conventional asymmetric converter. The charged high voltage is supplied to the phase winding for fast current build- up, and demagnetization current is charged to additional capacitor of 4-level inverter. In addition, a precise excitation position generator can reduce turn-on and turn-off angle error according to sampling period of digital control system. The proposed high speed SRM drive system is verified by computer simulations and experimental results.
Fatigue Life Estimation of Cold Drawn Contact Wire
Guo, Zhen,Kim, Yong-Seok,Hong, Suk-Woo,Li, Hao-Chuang,Koo, Jae-Mean,Seok, Chang-Sung,Lee, Ki-Won,Kwon, Sam-Young Korean Society for Precision Engineering 2014 International Journal of Precision Engineering and Vol.15 No.11
To evaluate the bending fatigue characteristics of contact wire, a stroke-based bending fatigue tester on contact wire has been developed by Kang et al. But this tester is too cumbersome and complicated. This paper is investigated with a new fatigue life estimation method based on Juvinall's method for estimation of S-N curve, which is widely used in steel structure, in order to estimate the bending S-N curve of cold drawn contact wire. First, the ultimate tensile strength and the axial tension fatigue test was performed with standard specimens, and the bending fatigue life for the cold drawn contact wire structure was predicted by using an improved S-N curve prediction method. Finally, the tested bending fatigue life of the structure was compared with the fatigue life estimated by the new method. As the result, the predicted bending S-N curve of the contact wire agreed fairly well with the experimental bending fatigue lives using the S-N curve and ultimate tensile strength of cold drawn material.
Experimental Study of Steel Plate Composite Shear Wall Units under Cyclic Load
Zhen Guo,Yingshu Yuan 한국강구조학회 2015 International Journal of Steel Structures Vol.15 No.3
A novel type of steel plate composite shear wall that was assembled by using a steel plate and precast cement-based concrete plate is presented in this paper. The steel plate shear wall, which differs from normal steel plate shear walls, was trilaterally constrained with an elastic restraint side. The precast concrete slab was designed to prevent steel plate buckling. Six steel plate shear wall specimens were tested by using a hydraulic servo actuator. The failure mode, shear resistance, lateral stiffness, and buckling mode were investigated through an experimental study. The results indicate that the width-thickness ratio of the steel plate affected the shear-carrying capacity and failure mode. A low width-thickness ratio of steel plate required adequate bonding to prevent boundary failure. The precast concrete slabs enhanced the lateral stiffness and improved the buckling strength or shear resistance of the steel plate. The material workable capability of steel plate was fully developed with a composite buckling-restraint by using the composite shear wall; similarly, the earthquake-resistant behavior of the structural system would likewise be enhanced further.
( Zhen Lin ),( Hedong Han ),( Wei Guo ),( Xin Wei ),( Zhijian Guo ),( Shujie Zhai ),( Shuai Li ),( Yiming Ruan ),( Fangyuan Hu ),( Dongdong Li ),( Jia He ) 대한내과학회 2021 The Korean Journal of Internal Medicine Vol.36 No.6
Background/Aims: To evaluate temporal trends of atrial fibrillation (AF) prevalence in critically ill patients who received prolonged mechanical ventilation (MV) in the United States. Methods: We used the 2008 to 2014 National Inpatient Sample to compute the weighted prevalence of AF among hospitalized adult patients on prolonged MV. We used multivariable-adjusted models to evaluate the association of AF with clinical factors, in-hospital mortality, hospitalization cost, and length of stay (LOS). Results: We identified 2,578,165 patients who received prolonged MV (21.27% of AF patients). The prevalence of AF increased from 14.63% in 2008 to 24.43% in 2014 (p for trend < 0.0001). Amongst different phenotypes of critically ill patients, the prevalence of AF increased in patients with severe sepsis, asthma exacerbation, congestive heart failure exacerbation, acute stroke, and cardiac arrest. Older age, male sex, white race, medicare access, higher income, urban teaching hospital setting, and Western region were associated with a higher prevalence of AF. AF in critical illness was a risk factor for in-hospital death (odds ratio, 1.13; 95% confidence interval, 1.11 to 1.15), but in-hospital mortality in critically ill patients with AF decreased from 11.6% to 8.3%. AF was linked to prolonged LOS (2%, p < 0.0001) and high hospitalization cost (4%, p < 0.0001). LOS (-1%, p < 0.0001) and hospitalization cost (-4%, p < 0.0001) decreased yearly. Conclusions: The prevalence of comorbid AF is increasing, particularly in older patients. AF may lead to poorer prognosis, and high-quality intensive care is imperative for this population.
Fire Resistances of Restrained Steel Beams Subjected to Fire Loads
Zhen Guo,Rui Gao,Xuecheng Zhang,Xingzhi Jia 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.8
Conventional fire loads and fire resistances of a steel beam still lack an adequate correlation. This paper has established therelationship between the responses of restrained steel beams and fire actions by using a new definition of fire resistances and a newexpression of fire loads. By using reduction factors of elastic modulus and yield strengths, has presented three critical equations topredict the limit state of a restrained steel beam in a fire. Based on these equations and the heat transfer formula, the paper provided anew definition of fire resistances. By using the heat release rate and effective rate coefficient of thermal absorption, a new expressionof fire loads has been argued. Compared with tests, the proposed approach in this paper is in good agreement with the measuredvalues in tests. The results show that the new fire resistances could be able to reflect the facts of heat transfers and duration time. Incontrast to conventional fire loads, the new fire loads are more efficient to indicate a fire load.
Effect of Molar Ratios on Compressive Strength of Modified Magnesium Oxysulfate Cement
Zhen-guo Li,Ze-sheng Ji 보안공학연구지원센터 2015 International Journal of Hybrid Information Techno Vol.8 No.6
To determine the effect of molar ratios on compressive strength of magnesium oxysulfate cement (MOS), the hardened MOS cement pastes mixed with different molar ratios of MgO/MgSO4 and H2O/MgSO4 were tested on the compressive strength. The examinations of strength development, phase compositions and microstructure of MOS cement are discussed in detail. The results show that these starting materials can significantly affect the compressive strength of MOS cement. The mixture with higher molar ratio of MgO/MgSO4 and lower molar ratio of H2O/MgSO4 can produce more 5Mg(OH)2 ·MgSO4·7H2O(517 phase) and less Mg(OH)2, which benefits the compressive strength of MOS cement.
Guo Zhen,Tong Di,Zhao Yan-cheng,Chen Shuang,Nai Ji-qiu,Ye Ming-hao 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.1
Asynchronous motor is widely used in various industrial fields. When asynchronous motor works in case close to the rated load, it will run at maximum efficiency. However, most of the load is 50–100% of rated load and it will lead to the serious waste of energy. This paper proposes an efficiency optimization control strategy based on the grey wolf optimization algorithm to improve the operating efficiency of asynchronous motors at light loads. The motor loss model considering the change of iron loss is established and it makes the asynchronous motor model more accurate. The grey wolf optimization algorithm is used to find the optimized flux value. When the asynchronous motor operates at the optimal flux, the loss power of the motor is decreased and the operation efficiency improves effectively. The proposed method reduces the flux search time and improves the stability of the system. The simulation model is established and the simulation results are provided to verify the feasibility of the proposed control strategy achieving the global efficiency optimum of asynchronous motor.