Browsing by Author "Zhang, Wei"

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    Compound hydrometeorological extremes: drivers, mechanisms and methods
    (Frontiers, 2021-10-13) Zhang, Wei; Luo, Ming; Gao, Si; Chen, Weilin; Hari, Vittal; Khouakhi, Abdou
    Compound extremes pose immense challenges and hazards to communities, and this is particularly true for compound hydrometeorological extremes associated with deadly floods, surges, droughts, and heat waves. To mitigate and better adapt to compound hydrometeorological extremes, we need to better understand the state of knowledge of such extremes. Here we review the current advances in understanding compound hydrometeorological extremes: compound heat wave and drought (hot-dry), compound heat stress and extreme precipitation (hot-wet), cold-wet, cold-dry and compound flooding. We focus on the drivers of these extremes and methods used to investigate and quantify their associated risk. Overall, hot-dry compound extremes are tied to subtropical highs, blocking highs, atmospheric stagnation events, and planetary wave patterns, which are modulated by atmosphere-land feedbacks. Compared with hot-dry compound extremes, hot-wet events are less examined in the literature with most works focusing on case studies. The cold-wet compound events are commonly associated with snowfall and cold frontal systems. Although cold-dry events have been found to decrease, their underlying mechanisms require further investigation. Compound flooding encompasses storm surge and high rainfall, storm surge and sea level rise, storm surge and riverine flooding, and coastal and riverine flooding. Overall, there is a growing risk of compound flooding in the future due to changes in sea level rise, storm intensity, storm precipitation, and land-use-land-cover change. To understand processes and interactions underlying compound extremes, numerical models have been used to complement statistical modeling of the dependence between the components of compound extremes. While global climate models can simulate certain types of compound extremes, high-resolution regional models coupled with land and hydrological models are required to simulate the variability of compound extremes and to project changes in the risk of such extremes. In terms of statistical modeling of compound extremes, previous studies have used empirical approach, event coincidence analysis, multivariate distribution, the indicator approach, quantile regression and the Markov Chain method to understand the dependence, greatly advancing the state of science of compound extremes. Overall, the selection of methods depends on the type of compound extremes of interests and relevant variables.
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    Dynamic analysis on single-rotor multi-input helicopter main gearbox related with structural parameters
    (Sage, 2019-09-26) Zhang, Wei; An, Luling
    Combined with the finite element method and the lumped mass method, the integral node dynamic model of a single-rotor multi-input helicopter main gearbox is established. The influence of shaft parameters on dynamic characteristics is analyzed, and each torsional shaft is regarded as a finite element node to derive the system dynamic equation. In addition, the dynamic model of the meshing pair element is established by lumped mass method, and these elements not only include internal excitations such as time-varying meshing stiffness and transmission error, but also carry the external load. The differential equations of the system are solved by the Fourier series method. The dynamic responses of the converging element and the planetary gear train are obtained. The load-sharing coefficients of these elements are calculated by the influence of the shaft structural parameters. A parameter optimization method is proposed to improve the system load characteristics, which provides a theoretical support for the design of helicopter main transmission system
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    Emerging contaminants: a One Health perspective
    (Cell Press, 2024-03-13) Wang, Fang; Xiang, Leilei; Leung, Kelvin Sze-Yin; Elsner, Martin; Zhang, Ying; Guo, Yuming; Pan, Bo; Sun, Hongwen; An, Taicheng; Ying, Guangguo; Brooks, Bryan W.; Hou, Deyi; Helbling, Damian E.; Sun, Jianqiang; Qiu, Hao; Vogel, Timothy M.; Zhang, Wei; Gao, Yanzheng; Simpson, Myrna J.; Luo, Yi; Chang, Scott X.; Su, Guanyong; Wong, Bryan M.; Fu, Tzung-May; Zhu, Dong; Jobst, Karl J.; Ge, Chengjun; Coulon, Frederic
    Environmental pollution is escalating due to rapid global development that often prioritizes human needs over planetary health. Despite global efforts to mitigate legacy pollutants, the continuous introduction of new substances remains a major threat to both people and the planet. In response, global initiatives are focusing on risk assessment and regulation of emerging contaminants, as demonstrated by the ongoing efforts to establish the UN’s Intergovernmental Science-Policy Panel on Chemicals, Waste, and Pollution Prevention. This review identifies the sources and impacts of emerging contaminants on planetary health, emphasizing the importance of adopting a One Health approach. Strategies for monitoring and addressing these pollutants are discussed, underscoring the need for robust and socially equitable environmental policies at both regional and international levels. Urgent actions are needed to transition toward sustainable pollution management practices to safeguard our planet for future generations.
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    General expression of poly(methyl methacrylate) optical fiber Bragg grating sensing response
    (IEEE, 2018-12-25) Zhang, Wei; Webb, D. J.
    Poly(methyl methacrylate) (PMMA) optical fiber inherently responds to the changes of temperature and relative humidity. PMMA optical fiber Bragg grating (POFBG) has been reported with diverse temperature and relative humidity sensitivities. These results cannot present the full performance of a POFBG sensor, as they are measured at limited environmental conditions. In this letter, we systematically investigated the POFBG temperature and relative humidity sensing responses. We found that POFBG temperature/relative humidity sensitivity is the function of both temperature and relative humidity. In the experiments, POFBG sensing responses vary linearly with temperature/relative humidity at fixed relative humidity/temperature. Based on this linearity, a general expression of POFBG sensing response to temperature and relative humidity has been obtained and verified for the first time to describe the POFBG performance in the desired operation range. The anisotropy in POF induced by drawing history could induce uncertainty in POFBG response but pre-straining POFBG overcomes this problem.
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    Ground-water monitoring using polymer optical fibre Bragg gratings
    (SPIE, 2019-08-28) Mehravar, M.; Yang, H.; Zhang, Wei; Webb, D. J.
    Optical fibre Bragg grating sensors inscribed in polymer optical fibre have been shown to be sensitive to the water content of the medium surrounding the fibre and this property has been applied, for example, to the monitoring of humidity and the water content of aviation fuel. In this work we assess the feasibility of using such sensors for monitoring the saturation of soils, which is important for civil engineering applications. We find a very non-linear response, with a rapid increase in Bragg wavelength as the water content increases from 0 to 0.5%, with a much more gradual, but still monotonic, increase thereafter. We speculate on the causes of this response.
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    Measuring water activity of aviation fuel using a polymer optical fiber Bragg grating
    (Society of Photo-optical Instrumentation Engineers, 2014-06-02) Zhang, Wei; Webb, David J.; Carpenter, Mark D.; Williams, Colleen
    Poly(methyl methacrylate) (PMMA) based polymer optical fiber Bragg gratings have been used for measuring water activity of aviation fuel. Jet A-1 samples with water content ranging from 100% ERH (wet fuel) to 10 ppm (dried fuel), have been conditioned and calibrated for measurement. The PMMA based optical fiber grating exhibits consistent response and a good sensitivity of 59±3pm/ppm (water content in mass). This water activity measurement allows PMMA based optical fiber gratings to detect very tiny amounts of water in fuels that have a low water saturation point, potentially giving early warning of unsafe operation of a fuel system
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    Microstructure-sensitive estimation of small fatigue crack growth in bridge steel welds
    (Elsevier, 2018-03-15) Yuan, Hao; Zhang, Wei; Castelluccio, Gustavo M.; Kim, Jeongho; Liu, Yongming
    A probabilistic finite element model is implemented to estimate microstructurally small fatigue crack growth in bridge steel welds. Simulations are based on a microstructure-sensitive crystal plasticity model to quantify fatigue indicator parameters (FIPs) at the slip system level and a fatigue model that relates FIPs to fatigue lives of individual grains. Microstructures from three weld zones, namely, fusion zone (FZ), heat affected zone (HAZ), and base metal (BM), are constructed based on their microstructural attributes such as grain morphology, size, and orientation. Statistical volume elements (SVEs) are generated and meshed independently for the three welding zones. Each grain within the SVEs is divided into several slip bands parallel to crystallographic planes. During the loading process, cracks nucleate at the slip bands (SBs) with the largest FIP next to the free surface. The crack extension path is assumed to be transgranular along SBs and the number of cycles required to crack the neighbor grain is calculated by the corresponding FIP-based crack growth rate equation. The simulation process is carried out using ABAQUS with a user defined subroutine UMAT for crystal plasticity. After the calibration of the constitutive model and irreversibility parameters, numerical simulations for small crack growth in three zones are presented. The crack length vs. the predicted fatigue resistance shows significant differences in the mean values and variability among the three weld zones.
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    Optimisation for clamping force of aircraft composite structure assembly considering form defects and part deformations
    (Hindawi Publishing Corporation / SAGE, 2021-04-15) Zhang, Wei; An, Luling; Chen, Yuan; Xiong, Yeping; Liao, Yabing
    Given the existence of manufacturing defects and the accumulation of assembly errors, non-compliant assembly appears between components, especially for composite structure assembly. In the engineering application, the clamping force (CF) is often used to eliminate the clearance between mating components, but the improper CF may result in unwanted structure failure. Thus, on the premise of ensuring the safety of composite parts, this study proposes a procedure to systematically optimise the assembly CF. Firstly, the components mating surfaces were obtained by laser scanner, and the matching of actual surfaces was transformed and simplified based on ‘equivalent surface’ concept. Then, a mathematical optimisation model was established. The CF layout and magnitude were taken as variables, and the clearance elimination rate and the overall assembly force value were employed as objective functions. Finally, the improved genetic algorithm (GA) was used to solve this problem. A parametric finite element analysis (FEA) model was built, and model accuracy was verified by physical experiments. The finite element calculation and post-processing were carried out by Python script in ABAQUS®. Compared to the engineer’s traditional approach, the influence of form defects and part deformations were considered, which can help control the assembly stress well and ensure product performance.
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    Performance degradation and component deterioration degree estimation for a turboshaft engine [Chinese language]
    (Zhongguo Hangkong Xuehui,Chinese Society of Aeronautics and Astronautics, 2015-11-30) Huang, Kai-Ming; Li, Yi-Guang; Zhang, Wei; Feng, Xing; Cai, Jiang-bing
    To monitor the performance and health conditions of a turboshaft engine during an endurance test, an engine mathematical model was set up and adapted to its real performance by adjusting component maps using a multiple-point performance adaption method. Gas path diagnostic analysis of the engine based on a non-linear gas path analysis (GPA) methodology was performed. In combination with field experiences, evaluation of the engine gas path component deterioration during an engine endurance test was carried out. The results indicated that the engine performance deviation and component deterioration varied over time. During initial phase of the test, the performance of the compressor and the compressor turbine deviated most rapidly then stabilized afterwards. As for the power turbine, the health was almost unchanged during the entire endurance test. The validation and experience of the GPA diagnostic technique prove that the technology can be applied into engine performance and health check for the evaluation of health of the turboshaft engine in its future service
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    Performances of PMMA-based optical fiber bragg grating sensor in extended temperature range
    (MDPI, 2021-05-23) Zhang, Wei; Webb, David J.
    PMMA based optical fiber Bragg grating (POFBG) sensors are investigated in an environmental chamber with controlled temperature and relative humidity at temperature extended to 70 °C. At below a critical temperature of 50 °C the POFBG sensor exhibits good linearity and sensitivity for both temperature and humidity sensing. Nonlinear responses are observed at higher temperature, giving rise to varying, reduced magnitudes of sensitivities. An important feature of POFBG humidity sensing is observed at above critical temperature where the POFBG humidity sensitivity turns from positive to negative. A theoretical model based on Lorentz–Lorenz equation is presented to estimate the dependence of POFBG refractive index on temperature and relative humidity. The experimental results qualitatively agree with the theoretical analyses
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    Posture optimization algorithm for large structure assemblies based on skin model
    (Hindawi, 2018-10-18) Zhang, Wei; An, Luling; Sherar, Peter; Tian, Wei
    Geometric deviations inevitably occur in product manufacturing and seriously affect the assembly quality and product functionality. Assembly simulations on the basis of computer-aided design (CAD) package could imitate the assembly process and thus find out the design deficiencies and detect the assemblability of the components. Although lots of researches have been done on the prediction of assembly variation considering the geometric errors, most of them only simplify the geometric variation as orientation and position deviation rather than the manufacturing deformation. However, in machinery manufacturing, even if the manufacturing defects are limited, they could propagate and accumulate through components and lead to a noncompliant assembly. Recently, many point-based models have been applied to assembly simulation; however they are mainly interested in simulating the resulting positions of the assembled parts and lack the consideration of the postprocessing after positioning. This paper enriches the complete assembly simulation process based on skin model and presents a simple and effective posture evaluation and optimization method. The studied approach includes a software algorithm applied to evaluate the contact state of the assembly parts and a mathematical model based on the particle swarm optimization to acquire the optimal assembly posture. To verify the efficiency and feasibility of the proposed method, a case study on the aircraft wing box scaling model assembly is performed.
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    Water content detection in aviation fuel by using PMMA based optical fiber grating
    (Elsevier, 2018-11-28) Zhang, Wei; Lao, Liyun; Hammond, David; Carpenter, Mark; Williams, Colleen
    Water in aviation fuel is a destructive contaminant and can cause serious problems that compromise aircraft’s safe operation and reduce its efficiency and lifetime. Online monitoring of water content in aviation fuel would permit the control of water content before it builds up to dangerous level. Optical fibers made of PMMA have water affinity. In a PMMA based optical fiber Bragg grating (POFBG) its refractive index and volume vary with the water content. This feature is used to detect tiny water content in aviation fuel in this work. The sensing mechanism of POFBG is analyzed. POFBG wavelength is found to be the function of both temperature and equilibrium relative humidity (ERH). POFBG response to water content in fuel can be determined by the ERH. The sensor is experimented at different environmental conditions to identify its sensitivity. As a result, a general expression of POFBG response is achieved. Water content in Jet-A1 is measured by using POFBG sensor calibrated with both environmental chamber and coulometric titration. POFBG sensor is finally tested in a simulation fuel tank, demonstrating a better performance than coulometric titration. A sensitivity of POFBG wavelength change to water content of 33 pm/ppm is achieved at room temperature, indicating detectable water content of 0.03 ppm.