Browsing by Author "Liu, Yifei"

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Optimum design of a composite outer wing subject to stiffness and strength constraints
    (Cranfield University, 2011-01) Liu, Yifei; Guo, Shijun J.
    Composite materials have been more and more used in aircraft primary structures such as wing and fuselage. The aim of this thesis is to identify an effective way to optimize composite wing structure, especially the stiffened skin panels for minimum weight subject to stiffness and strength constraints. Many design variables (geometrical dimensions, ply angle proportion and stacking sequence) are involved in the optimum design of a composite stiffened panel. Moreover, in order to meet practical design, manufacturability and maintainability requirements should be taken into account as well, which makes the optimum design problem more complicated. In this thesis, the research work consists of three steps: Firstly, attention is paid to metallic stiffened panels. Based on the study of Emero’s optimum design method and buckling analysis, a VB program IPO, which employs closed form equations to obtain buckling load, is developed to facilitate the optimization process. The IPO extends the application of Emero’s method to an optimum solution based on user defined panel dimensional range to satisfy practical design constraints. Secondly, the optimum design of a composite stiffened panel is studied. Based on the research of laminate layup effects on buckling load and case study of bucking analysis methods, a practical laminate database (PLDB) concept is presented, upon which the optimum design procedure is established. By employing the PLDB, laminate equivalent modulus and closed form equations, a VB program CPO is developed to achieve the optimum design of a composite stiffened panel. A multi-level and step-length-adjustable optimization strategy is applied in CPO, which makes the optimization process efficient and effective. Lastly, a composite outer wing box, which is related to the author’s GDP work, is optimized by CPO. Both theoretical and practical optimum solutions are obtained and the results are validated by FE analysis.
  • Thumbnail Image
    ItemOpen Access
    Silver nanoparticles confined in shell-in-shell hollow TiO2 manifesting efficiently photocatalytic activity and stability
    (Elsevier, 2019-02-18) Zhao, Shidong; Chen, Juanrong; Liu, Yifei; Jiang, Ying; Jiang, Caiguo; Yin, Zhengliang; Xiao, Yingguan; Cao, Shunsheng
    The complete degradation of tetracycline still is a challenge for TiO2-based photocatalysts under simulated solar light irradiation. To tackle this challenge, we devise Ag nanoparticles (Ag NPs) confined in shell-in-shell hollow TiO2 photocatalyst (HTAT). This strategy mainly involves the construction of CPS@TiO2 core-shell composites, the form of TiO2 inner shell, AgNPs loading by photo-deposition, the assembly of TiO2 outer shell, and phase transition of anatase TiO2 by calcination at 450℃. All characterizations including TEM, STEM Mapping, BET, and XPS confirm the unique structure of the as-synthesized HTAT photocatalyst. As expected, the complete degradation of tetracycline (TC and TCH) can be realized by using HTAT photocatalyst under simulated solar light irradiation because its TiO2 two shells simultaneously take part in the photodegrading reaction of TC or TCH. The transformation intermediates and degradation pathway were analyzed by LC/MS. Our work effectively overcomes the disadvantages of many previously reported TiO2-based photocatalysts for the incomplete degradation of tetracycline.