Browsing by Author "Department of Mechanical and Energy Engineering, School of Engineering and Technology"

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    Analysis of a hydrostatic drive wind turbine for improved annual energy production
    (AIMS Press, 2018-10-21) Deldar, Majid; Izadian, Afshin; Anwar, Sohel; Department of Mechanical and Energy Engineering, School of Engineering and Technology
    This paper presents an analysis on ways to improve the annual energy production (AEP) of a wind turbine utilizing a drivetrain that operates based on the hydrostatic transmission. The system configuration of such a drivetrain is explained in details and a comparison of operation and characteristics with existing drivetrains is provided. AEP was estimated for these configurations through appropriate dynamic modeling and operational efficiency optimization. Optimal selection of a number of design variables and system parameters contributed to the improvements in the AEP. Findings of this study demonstrate that the proposed hydrostatic drivetrain improves the AEP of a 750 kW turbine by up to +8% when compared with a geared wind turbine. The AEP improvements of the hydrostatic drive wind turbine were more than 10% for a 1.5 MW system over geared configuration. It is also demonstrated that the efficiency of power generation can be improved under various wind speeds. The suitable selection of synchronous speed of the generator directly improves the efficiency of operation by up to 35% at low wind speeds. An efficiency improvement was also observed under higher operating pressures and longer turbine blades.
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    Role of disordered bipolar complexions on the sulfur embrittlement of nickel general grain boundaries
    (Nature Research, 2018-07-17) Hu, Tao; Yang, Shengfeng; Zhou, Naixie; Zhang, Yuanyao; Luo, Jian; Department of Mechanical and Energy Engineering, School of Engineering and Technology
    Minor impurities can cause catastrophic fracture of normally ductile metals. Here, a classic example is represented by the sulfur embrittlement of nickel, whose atomic-level mechanism has puzzled researchers for nearly a century. In this study, coupled aberration-corrected electron microscopy and semi-grand-canonical-ensemble atomistic simulation reveal, unexpectedly, the universal formation of amorphous-like and bilayer-like facets at the same general grain boundaries. Challenging the traditional view, the orientation of the lower-Miller-index grain surface, instead of the misorientation, dictates the interfacial structure. We also find partial bipolar structural orders in both amorphous-like and bilayer-like complexions (a.k.a. thermodynamically two-dimensional interfacial phases), which cause brittle intergranular fracture. Such bipolar, yet largely disordered, complexions can exist in and affect the properties of various other materials. Beyond the embrittlement mechanism, this study provides deeper insight to better understand abnormal grain growth in sulfur-doped Ni, and generally enriches our fundamental understanding of performance-limiting and more disordered interfaces.