291 research outputs found
Xi ju zi ben lun.
No full text馬克思原著;阪本勝編劇;費明君翻譯.Makesi yuan zhu ; Banben Sheng bian ju ; Fei Mingjun fan yi
Fan ti zi he jian ti zi du zhe zai yue du zhong de cha yi
No full textZhai, Mingjun.Thesis M.Phil. Chinese University of Hong Kong 2014.Includes bibliographical references (leaves 64-68).Abstracts also in Chinese.Title from PDF title page (viewed on 30, September, 2016).Zhai, Mingjun
Remaining Useful Life Estimation of Fan Slewing Bearings in Nonlinear Wiener Process with Random Covariate Effect
No full textSince the degradation process of fan slewing bearings is easily influenced by the external environment, it is difficult to estimate its remaining useful life (RUL) accurately. A nonlinear Wiener degradation model considering the influence of random covariate is established for the prediction of the RUL of fan slewing bearings in this study. Firstly, considering the nonlinear and nonmonotonic properties of the operation process of fan slewing bearings, the degradation model of the nonlinear Wiener process of fan slewing bearings is established. Secondly, the combination of random covariate models and the nonlinear Wiener degradation process is researched. The stress effect which is used as a random covariate is introduced into the nonlinear Wiener degradation model in the form of the additive hazard model. Moreover, the closed expression for the RUL probability density function(PDF) is derived for the random variation of drift coefficients, the individual differences and the random variation of covariates. Thirdly, the maximum likelihood estimation algorithm is used to estimate the RUL parameters depending on the historical degradation data. Finally, the vibration data of fan slewing bearings monitored by sensors are used to verify the effectiveness of the proposed method. The results show that the proposed method can be used to improve the fitting degree of the model and the accuracy of RUL estimation
New Insights into Flow for a Low-Bypass-Ratio Transonic Fan with Optimized Rotor
No full textIn this paper, a three-dimensional aerodynamics optimization system is built and applied to optimize a rotor blade to balance the conflicts between stall margin, total pressure ratio, adiabatic efficiency, and mass flow rate for the high-loading and transonic-flow fan. A novel flow diagnostic method based on vorticity dynamics theory is utilized to analyze the reasons for the improvement in aerodynamic performance in the optimized transonic fan. In the established aerodynamic optimization method, use the blade profile camber line curvature and its leading edge metal angle as the optimization variables, which are optimized by modifying the coordinates of their control points and introducing a genetic algorithm. Finally, the vorticity dynamics parameters, such as the boundary vorticity flux (BVF), azimuthal vorticity and skin-friction lines are used to diagnose the key flow features in the optimized and baseline fan passage. The results indicate that, by controlling skillfully the blade camber line curvature in the optimization improves the aerodynamic performance of the fan stage, increasing the total pressure ratio by 1.90% while increasing the mass flow rate and adiabatic efficiency by 5.82% and 4.45%, respectively. The formulas from the vorticity dynamics diagnosis method indicate a close link between the aerodynamic performance and vorticity dynamic parameters for the axial fan/compressor passage flow, and that both azimuthal vorticity and boundary vorticity flux have significant influence on fan stage performance. Moreover, the boundary layer separation flow on the rotor blade surface is accompanied by a spike of entropy and static pressure, and their derivative/gradient also suffer drastic changes under the effect of shock waves. Detailed flow information can be obtained about the on-wall with high accuracy based on the vorticity dynamics diagnosis method, which provides researchers with a novel method for the turbomachinery aerodynamic design and analysis in the aero-engine engineering development field
Multi-Sensor Information Fusion and Multi-Model Fusion-Based Remaining Useful Life Prediction of Fan Slewing Bearings with the Nonlinear Wiener Process
No full textMany factors affect the accuracy of the estimation of the remaining useful life (RUL) of the fan slewing bearings, thereby limiting the sustainable development of the wind power industry. More specifically, the traditional vibration data, which are easily disturbed by noises, cannot comprehensively characterize the health status; thus, the physical model is difficult to establish, and when the data-driven model analyzes the status, it results in unclear physical mechanisms. A new nonlinear Wiener degradation model was established based on the fusion of the physical models and the data-driven models, which was employed to characterize the degradation process of the slewing bearings in this work, and for the local temperature distribution, which has a strong anti-interference ability, the multi-sensor temperature data fusion was selected to analyze the RUL prediction. First, the multi-sensor temperature data were fused by performing a principal component analysis (PCA) to obtain the comprehensive health index (CHI), which represents the fan slewing bearings. Second, the Arrhenius Equation, which characterizes the degradation using temperature, was introduced into the nonlinear Wiener model, and a new degradation model was established. Moreover, considering the random change of the drift coefficients and the individual differences, the closed expression of the probability density function (PDF) of RUL was derived. Third, maximum likelihood estimation (MLE) was used to estimate the parameters. In addition, Bayesian analysis was used to update parameters to achieve real-time estimation. The results demonstrated that the proposed method can be used to significantly improve the fitting degree of the model and the accuracy of RUL estimation
Cai yong suan zi fen lie fa wei yi lan zi qi quan ding jia
No full textOr, Ming Chun = 採用算子分裂法為一籃子期權定價 / 柯銘駿.Thesis M.Phil. Chinese University of Hong Kong 2014.Includes bibliographical references (leaves 138-140).Abstracts also in Chinese.Title from PDF title page (viewed on 02, December, 2016).Or, Ming Chun = Cai yong suan zi fen lie fa wei yi lan zi qi quan ding jia / Ke Mingjun
Innovation Claudia and environmental Kuznets curve analysis.
No full textInnovation Claudia and environmental Kuznets curve analysis.</p
An Application of a Dual-Module VSG Based on QPR and Virtual Impedance in Three-Phase Unbalanced Power Grids
No full textAs an innovative solution, the virtual synchronous generator (VSG) facilitates the seamless incorporation of renewable energy into power grids. It also exhibits the ability to reconfigure system inertia and deliver damping effects, thereby assuming a progressively vital role in contemporary power systems. Three-phase voltage imbalance, a common phenomenon in power grids, causes current distortion. Imbalance, a common phenomenon in power grids, causes current distortion in VSG outputs, thereby affecting power quality. Therefore, ensuring symmetrical current injection into the grid has become a critical challenge in grid-connected technology. To resolve this challenge, a dual-module VSG control scheme is introduced, enabling precise regulation of the VSG’s power delivery. This approach effectively distinguishes and separately manages the positive-sequence and negative-sequence power outputs of the VSG. Furthermore, virtual impedance and quasi-PR control are incorporated into the current control loop to achieve zero negative-sequence power output from VSG, ensuring a stable power supply. Simulation results validate the reliability of this approach, providing both a theoretical foundation and practical evidence for its future application
The Tax Disadvantage Of Ordinary Income: An Event Study On The Legislative Process Of JGTRRA
No full textThe Jobs Growth and Tax ReliefReconciliation Act of 2003 (JGTRRA), signed into law by President George W.Bush, was a significant legislation in recent tax history. As the tax rates on capital gains anddividends are reduced to a historical low of 15%, U.S. stock prices haveincreased and the cost of equity capital declined after its passage. In contrast to the dividends and capital gainsthat receive preferential tax rates under JGTRRA, yields from U.S. Treasurybill remain tax-disadvantaged as ordinary income at a top marginal rate of 35%. Using an event study approach based ontwo years of Treasury yield observations, the author examines Treasury yield reactionsto major legislative events surrounding the passage of JGTRRA. The result suggests that a tax policyintentionally favoring dividends and capital gains over ordinary income may unintentionallypush up yields in the Treasury bill market, thereby affecting the cost ofgovernment borrowing
Algorithms and applications of preference based ranking for information retrieval
No full textIn this thesis, the author designed three sets of preference based ranking algorithms for information retrieval and provided the corresponsive applications for the algorithms. The main goal is to retrieve recommended, high similar and valuable ranking results to users
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