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RISS 인기검색어
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- 저자 : Zhendong Xu (검색결과 5 건)
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Assessment of across-wind responses for aerodynamic optimization of tall buildings
Xu, Zhendong,Xie, Jiming Techno-Press 2015 Wind and Structures, An International Journal (WAS Vol.21 No.5
A general approach of aerodynamic optimization of tall buildings is presented in this paper, focusing on how to best compromise wind issues with other design aspects in the most efficient manner. The given approach is reinforced by establishing an empirical method that can quickly assess the across-wind loads and accelerations as a function of building frequencies, building dimensions, aspect ratios, depth-to-width ratios, and site exposures. Effects of corner modifications, including chamfered corner and recessed corner, can also be assessed in early design stages. Further, to assess the effectiveness of optimization by tapering, stepping or twisting building elevations, the authors introduce a method that takes use of sectional aerodynamic data derived from a simple wind tunnel pressure testing to estimate reductions on overall wind loads and accelerations for various optimization options, including tapering, stepping, twisting and/or their combinations. The advantage of the method is to considerably reduce the amount of wind tunnel testing efforts and speed up the process in finding the optimized building configurations.
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Assessment of across-wind responses for aerodynamic optimization of tall buildings
Zhendong Xu,Jiming Xie 한국풍공학회 2015 Wind and Structures, An International Journal (WAS Vol.21 No.5
A general approach of aerodynamic optimization of tall buildings is presented in this paper, focusing on how to best compromise wind issues with other design aspects in the most efficient manner. The given approach is reinforced by establishing an empirical method that can quickly assess the across-wind loads and accelerations as a function of building frequencies, building dimensions, aspect ratios, depth-to-width ratios, and site exposures. Effects of corner modifications, including chamfered corner and recessed corner, can also be assessed in early design stages. Further, to assess the effectiveness of optimization by tapering, stepping or twisting building elevations, the authors introduce a method that takes use of sectional aerodynamic data derived from a simple wind tunnel pressure testing to estimate reductions on overall wind loads and accelerations for various optimization options, including tapering, stepping, twisting and/or their combinations. The advantage of the method is to considerably reduce the amount of wind tunnel testing efforts and speed up the process in finding the optimized building configurations.
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A Study of the SPWM High-Frequency Harmonic Circulating Currents in Modular Inverters
Xu, Sheng,Ji, Zhendong The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6
Due to detection and control errors, some high-frequency harmonics with voltage-source characteristics cause circulating currents in modular inverters. Moreover, the circulating currents are usually affected by the output filters (OF) of each module due to their filter and resonance properties. The interaction among the circulating currents in the modules increase the power loss and reduce system stability and control precision. Therefore, this paper reports the results of a study on the SPWM high-frequency harmonics circulating currents for a double-module VSI. In the paper, an analysis of the circulating-current circuits is briefly described. Next, a mathematic model of the single-module output voltage based on the carrier frequency of SPWM is built. On this basis, through mathematic modeling of high-frequency harmonic circulating currents, the formation mechanism and distribution characteristics of circular currents and their influences are studied in detail. Finally, the influences of the OF on the circulating currents are studied by mainly taking an LC-type filter as an example. A theoretical analysis and experimental results demonstrate some important characteristics. First, the carrier phase shifting of the SPWM for each module is the major cause of the SPWM harmonic circulating currents, and the circulating currents are in an odd distribution around n-times the carrier frequency $n{\omega}_s$, where n = 1, 2, 3, ${\ldots}$. Second, the harmonic circular currents do not flow into the parallel system. Third, the OF can effectively suppress the non-circulating part of the high-frequency harmonic currents but is ineffective for the circulation part, and actually reduces system stability.
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A Study of the SPWM High-Frequency Harmonic Circulating Currents in Modular Inverters
Sheng Xu,Zhendong Ji 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6
Due to detection and control errors, some high-frequency harmonics with voltage-source characteristics cause circulating currents in modular inverters. Moreover, the circulating currents are usually affected by the output filters (OF) of each module due to their filter and resonance properties. The interaction among the circulating currents in the modules increase the power loss and reduce system stability and control precision. Therefore, this paper reports the results of a study on the SPWM high-frequency harmonics circulating currents for a double-module VSI. In the paper, an analysis of the circulating-current circuits is briefly described. Next, a mathematic model of the single-module output voltage based on the carrier frequency of SPWM is built. On this basis, through mathematic modeling of high-frequency harmonic circulating currents, the formation mechanism and distribution characteristics of circular currents and their influences are studied in detail. Finally, the influences of the OF on the circulating currents are studied by mainly taking an LC-type filter as an example. A theoretical analysis and experimental results demonstrate some important characteristics. First, the carrier phase shifting of the SPWM for each module is the major cause of the SPWM harmonic circulating currents, and the circulating currents are in an odd distribution around n-times the carrier frequency nωs, where n = 1, 2, 3, …. Second, the harmonic circular currents do not flow into the parallel system. Third, the OF can effectively suppress the non-circulating part of the high-frequency harmonic currents but is ineffective for the circulation part, and actually reduces system stability.
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Pore Structure of Ancient Chinese Bricks under Environmental Vicissitudes
Yongjing Tang,Zhendong Shao,Tianlong Xu 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.5
This paper studies the pore structures of ancient Chinese bricks. Two building groups consisting of seven ancient masonry buildings were examined: the Longmen Temple Group and Songyue Temple Group, both located in central China. The brick ages were examined by carbon-14 isotope measurements, the micro constituents by X-ray fluorescence experiments, and the pore structural characteristics by mercury intrusion porosimetry and saturation coefficient determination. The pore diameter rates of change were measured, calculated and analyzed. From the mercury intrusion porosimetry data, a linear relationship between the volume change of a sample and its age was determined for pores with diameters of 1-5 μm. The environmental vicissitudes caused the volumes of pores whose diameters are less than 1 μm to decrease and those of pores with diameters of 1-5 μm to increase. The change in the void volume as a function of pore size alters the material’s original porosity. Understanding the mechanics of how the pore structure of bricks changes over time sheds light on the relationship between material performance and environmental vicissitudes.
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