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11 results on '"Tang, Weihan"'

8. An Investigation into Energy Efficient Laboratory Equipments Freezers & Autoclaves

Author

Ma, Cheng-Li Jerry, Koochakyazdi, Sousan, Tang, Weihan, and Zhang, Frank

Abstract

Disclaimer: “UBC SEEDS provides students with the opportunity to share the findings of their studies, as well as their opinions, conclusions and recommendations with the UBC community. The reader should bear in mind that this is a student project/report and is not an official document of UBC. Furthermore readers should bear in mind that these reports may not reflect the current status of activities at UBC. We urge you to contact the research persons mentioned in a report or the SEEDS Coordinator about the current status of the subject matter of a project/report.”

Published
2010
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9. Seamless multi‐mode switching controller of four‐switch buck–boost converter based on integrated natural trajectory method.

Author

Chen, Zhangyong, Liu, Haifeng, Chen, Yong, Tang, Weihan, and Liu, Yunyan

Abstract

Summary With the characteristics of high efficiency and high power density, the four switch buck–boost (FSBB) converter is widely used in electric vehicles, direct current microgrids, and so forth. However, how to achieve smooth switching between different modes of FSBB has always been a hot issue in the theoretical and engineering fields. In this paper, considering the dynamic performance and output voltage or inductance current deviation, a control algorithm with integrated natural trajectory method is designed to realize the switching of different modes of FSBB converter. The proposed control algorithm is based on the theory of large signal natural locus and average natural locus. The normalized phase locus of inductance current and output voltage divides the phase plane into five regions and performs large signal or average switching operations in different regions. Theoretical analysis shows that the proposed control algorithm can achieve the balance between the dynamic performance and output voltage or inductance current deviation of FSBB converter in different mode switching. Finally, the performance of the proposed control algorithm is verified by experiments results. [ABSTRACT FROM AUTHOR]

Published
2024
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10. Nanoscale Characterization of V-Defect in InGaN/GaN QWs LEDs Using Near-Field Scanning Optical Microscopy.

Author

Li, Yufeng, Tang, Weihan, Zhang, Ye, Guo, Maofeng, Li, Qiang, Su, Xilin, Li, Aixing, and Yun, Feng

Subjects
*NEAR-field microscopy, *QUANTUM efficiency, *QUANTUM wells, *ATOMIC force microscopy, *CURRENT distribution
Abstract

The size of the V-defects in the GaN/InGaN-based quantum wells blue light-emitting diode (LED) was intentionally modified from 50 nm to 300 nm. High resolution photoluminescence and electroluminescence of a single large V-defect were investigated by near-field scanning optical microscopy. The current distribution along the {10-11} facets of the large defect was measured by conductive atomic force microscopy. Nearly 20 times the current injection and dominant emission from bottom quantum wells were found in the V-defect compared to its vicinity. Such enhanced current injection into the bottom part of quantum wells through V-defect results in higher light output power. Reduced external quantum efficiency droops were achieved due to more uniform carrier distribution. The un-encapsulated fabricated chip shows light output power of 172.5 mW and 201.7 mW at 400 mA, and external quantum efficiency drop of 22.3% and 15.4% for the sample without and with large V-defects, respectively. Modified V-defects provide a simple and effective approach to suppress the efficiency droop problem that occurs at high current injection, while improving overall quantum efficiency. [ABSTRACT FROM AUTHOR]

Published
2019
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11. Reduced-Order Modeling of Mistuned Bladed Disks in Contact with Dry Friction Ring Dampers

Author

Tang, Weihan

Subjects
Turbomachinery, Mistuning, Friction damping, Reduced-order modeling, Structural dynamics
Abstract

Bladed disks (blisks) used in turbomachinery applications frequently operate under severe forcing conditions, which can lead to high levels of dynamics responses and pre-mature high cycle fatigue (HCF). Small blade-to-blade variations in structural properties, referred to as mistuning, result in strain energy localization, drastically amplifying blisk forced responses, and accelerate HCF. To quantitatively capture the effect of mistuning, it is necessary to develop efficient computational methods to predict the free and forced responses of blisks with various types of mistuning patterns. Due to the high geometric complexity of commercial blisks, full-order finite element (FE) blisk models contain many degrees of freedom (DOFs). Direct structural analyses with such FE models are computationally cumbersome or practically infeasible. Moreover, to prevent blisks from reaching HCF, frictional damping sources are introduced to dissipate vibrational energy and reduce the level of forced responses. Frictional damping is nonlinear in nature, and adds complexity into the blisk systems. Thus, robust and accurate reduced-order models must be developed to predict fast the dynamic responses of blisks with various mistuning and frictional damping sources. The main objective of this study is to develop a framework that involves several novel reduced-order modeling techniques. This framework is capable of efficiently and accurately capturing linear and nonlinear dynamic responses of blisks with small blade material variations, large changes in blisk mass, stiffness, and geometry, and dry friction ring dampers. Moreover, this framework serves as a powerful tool in designing friction dampers with optimal design parameters.

Published
2017

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