Browsing by Author "Xie, Yanmei"

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    Hygrothermal Effects of Air Cavities Behind Claddings on Building Envelopes
    (North Dakota State University, 2022) Xie, Yanmei
    Air cavity behind claddings within building envelope provides an approach to mitigating building moisture-related issues as well as improving the building’s thermal performance. However, studies in literature commonly assume the cavity air as still and thus neglect the influence of mixed convection on the performance of building envelope. In addition, the drying performance of the air cavities remains unknown, and commonly a rectangular unicellular cavity is improperly assumed to simplify the investigation of the hygrothermal performance of a cladding system. Moreover, the literature lacks a study of the effect of humid air in the air cavity on heat and mass transfer. Therefore, it necessitates advanced problem formulation and solving to comprehensively study the effects of air cavities behind claddings on the performance of building envelope. The specific objectives are to 1) investigate potential of self-drying siding with raised air cavities for building envelopes; 2) study the effects of the cavity depth in mixed convection of air cavity for building envelopes; 3) analyze the effects of humid air in an air cavity on mass and heat transfer with phase change at the wall. To achieve these objectives, firstly, this study redefines the drying potential of air cavity taking into account the air cavity depth related to the shape irregularity and the inlet and outlet uncertainties. Then the formulated problems of mixed convection of air cavities behind sidings are solved with a perturbation method and SIMPLER algorithm. The results show that the drying performance is found to be heavily dependent on the cavity depth. Further, increasing the ratio of the siding depth to the air cavity depth amplifies the cavity air’s velocity, temperature, and mass fraction at cavity walls, as well as the heat and mass transfer across cavities. Consequently, this study demonstrated that humid air with the phase change and the cavity depth have the significant effects on the hygrothermal performance of building envelopes. The outcome of this study provides valuable guidance on the thermal performance evaluation of air cavity and has the potential of improving the design of claddings for the overall hygrothermal performance of building envelope.
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    Numerical Simulation and Structural Optimization of Composite Rigid Frame Bridge
    (North Dakota State University, 2017) Xie, Yanmei
    A composite rigid frame bridge replaces a certain portion of the concrete middle span of a bridge with a section of the steel girder. While the steel span improves the bending moment distribution of the rigid frame structure, it increases the stress level of certain cross-sections of the girder. There is little research reporting the effects of the addition of the steel span on the layout and structural design. This research studies the influence of the steel span on the structural behavior of the rigid frame bridge and conducts the structural optimization regarding the steel span ratio, curve order of the girder’s bottom line, and height-to-span ratio using the bending strain energy as the objective function. Finally, this study develops the computer program for structural analysis of composite rigid frame bridge structure using MATLAB, which can be used for advanced structural optimization.