Investigation on large turbo-generator stator end winding dynamic characteristics based on response surface method

Zhao, Yang,Xiao, Yang,Lu, Sheng,Sun, Hao,Huo, Wenhao,Liao, Yong The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.10

The natural frequencies corresponding to the particular mode shapes of a large turbo-generator must not be in the resonance region before delivery. Different parameters may clearly affect these dynamic characteristics. Different from other studies, this paper introduces a method for obtaining the inherent characteristics of end winding in a short period of time under multiple simultaneously changing parameters. The proposed process is based on the response surface method (RSM). In this method, the main concerned natural frequencies were taken as the critical index to describe the dynamic behaviors of the end winding, with which the mathematical relationship between the dynamic characteristics and design variables was analyzed. First, the stiffness of the rings, stiffness of the radial braces and number of pins bonded to the radial braces were used as samples for orthogonal experimental design. Then, the natural modes and frequencies of 25 different samples were acquired by conducting modal analysis with ABAQUS software. Utilizing these dynamic results, a second-order polynomial response surface model was established to describe the relationships between natural frequencies and these three different parameters. Then, the quality of this model was verified by calculating the valuating indexes for comparison with support vector regression (SVR). With the response surface model, the variation regularities of the natural frequencies and modes due to the above parameters were discussed. The method proposed in this paper can enable natural frequencies in the whole design space to be quickly determined without finite-element analysis, greatly improving the development efficiency and laying a foundation for dynamic response prediction during normal operation with different parameters and additional large turbo-generator stator end winding optimization.

Spectrum Allocation based on Auction in Overlay Cognitive Radio Network

( Wenhao Jiang ),( Wenjiang Feng ),( Yang Yu ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.9

In this paper, a mechanism for spectrum allocation in overlay cognitive radio networks is proposed. In overlay cognitive radio networks, the secondary users (SUs) must first sense the activity of primary users (PUs) to identify unoccupied spectrum bands. Based on their different contributions for the spectrum sensing, the SUs get payoffs that are computed by the fusion center (FC). The unoccupied bands will be auctioned and SUs are asked to bid using payoffs they earned or saved. Coalitions are allowed to form among SUs because each SU may only need a portion of the bands. We formulate the coalition forming process as a coalition forming game and analyze it by game theory. In the coalition formation game, debtor-creditor relationship may occur among the SUs because of their limited payoff storage. A debtor asks a creditor for payoff help, and in return provides the creditor with a portion of transmission time to relay data for the creditor. The negotiations between debtors and creditors can be modeled as a Bayesian game because they lack complete information of each other, and the equilibria of the game is investigated. Theoretical analysis and numerical results show that the proposed auction yields data rate improvement and certain fairness among all SUs.

Numerical Simulation of Edge Effect in Resin Transfer Molding for Plain-weave Fabric

Wenkai Yang,Shihong Lu,Wenhao Liu 한국섬유공학회 2020 Fibers and polymers Vol.21 No.9

Plain-weave fabric is a kind of fiber preform which has been commonly used in resin transfer molding (RTM) tomanufacture polymer composites. However, the edge area of plain-weave fabric is easy to shed yarns which will cause theuneven distribution of permeability between edge channel and center of mold in filling process of RTM. Meanwhile, theuneven distribution of permeability will cause the edge effect and seriously affect the final quality of composite materials. Inthis paper, a method to numerically calculate the permeability of edge channel which fully considers the edge area of plainweavefabric is proposed. The experiment and simulation of edge effect in filling process are performed. The results showthat the simulation of edge effect which applies the edge channel’s permeability calculated by this method are in goodagreement with the experimental results. The research in this paper is meaningful to improve the accuracy of edge effectsimulation so as to provide a reference for the design of mold structure.

H-Infinity Shifting Control in a Dual-Speed Transmission for Electric Vehicle

Tan Senqi,Yang Jue,Khajepour Amir,Zhao Xinxin,Yu Wenhao 한국자동차공학회 2021 International journal of automotive technology Vol.22 No.1

To improve the economic and comfort performance of pure electric vehicles (PEV), this paper proposes a novel H-infinity gear-shifting controller for dual-speed Transmissions (DST) to achieve a smooth and swift shifting when considering uncertain disturbances in system. Firstly, the structure as well as the working principle of the DST for PEV are introduced briefly and the mathematical model of the transmission is derived according to the Lagrange equation. Then the gear-shifting process is analyzed and the control problem is formulated according to the clutch status. Next, a robust Hinfinity controller is proposed to attenuate the vehicle jerk as well as the clutch sliding energy loss. Simulation results under different working conditions indicate the controller presented have better performance in limiting the effect of unknown external disturbances comparing to a calibrated proportional-integral derivative (PID) controller.

Hydrothermal Synthesis and Luminescent Properties of Uniform CaSnO[sub 3]:Eu[sup 3+] Microcrystals with Controlled Morphology

Fu, Zuoling,Li, Wenhao,Du, Shan,Yang, Hyun Kyoung,Jeong, Jung Hyun The Electrochemical Society 2009 Journal of the Electrochemical Society Vol.156 No.10

Synthesis, morphology and optical properties of SrTiO₃:Pr³⁺ phosphors

Fu, Zuoling,Li, Wenhao,Kyoung Yang, Hyun,Kee Moon, Byung,Chun Choi, Byung,Hyun Jeong, Jung Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139

<P>SrTiO<SUB>3</SUB>:Pr<SUP>3+</SUP> phosphors with different morphologies were prepared by using high-temperature solid-state reaction, the solvothermal method and sol–gel synthesis. All the products were systematically characterized by powder x-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), photoluminescence (PL) and photoluminescent excitation spectra (PLE). The influence of different synthesis methods on the morphology and optical properties of SrTiO<SUB>3</SUB>:Pr<SUP>3+</SUP> was discussed.</P>

Measuring (In)Attention to Mutual Fund Fees : Evidence from Experiments

Hugh H. Kim,Wenhao Yang 한국재무학회 2019 한국재무학회 학술대회 Vol.2019 No.05

We estimate investors' attention level to mutual fund fees based on a parsimonious asset allocation model with limited attention in an experimental setting. We find that, on average, investors allocate 62.5% of their full attention to mutual fund fees. We also find that cognitive ability is an important factor in determining investors' attention to the fees. The estimated attention level implies investors in the U.S. mutual funds market pay $16 billion more in fees per year than the level they recognize. We evaluate policy options to increase attention to fees and find that the policy effectiveness may depend on one's cognitive ability.

The luminescence properties and thermal stability of a green-blue color tunable Sr2SiO4: Tb3+, Ce3+ phosphor

Tianpeng Yu,Lixi Wang,Xiaojuan Yang,Wenhao Ding,Qitu Zhang 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.1

In this paper, green-blue emitting Sr 2 SiO 4 (SSO):0.03Tb 3+ , x Ce 3+ ( x = 0–0.005) materials were synthesized via a solid-statereaction method. The crystal structures, luminescence properties, decay time, and thermal stability were measured in thiswork. The as-prepared phosphors exhibit both an indigo emission of Ce 3+ and green emission of Tb 3+ with considerableintensity ( λ ex = 300 nm). Tb 3+ ion emission was intensifi ed obviously with co-doping Ce 3+ . The luminescence spectra ofSr 2 SiO 4 (SSO):0.03Tb 3+ , Ce 3+ shows characteristic line of Tb 3+ ion transition ( 5 D 4 → 7 F 5 ). Tunable green-blue color canbe obtained by the addition of Ce 3+ ions. An eff ective energy transfer process between Tb 3+ and Ce 3+ was supposed andconfi rmed from decay curves. In addition, the energy transfer mechanism from Ce 3+ to Tb 3+ ions in the Sr 2 SiO 4 (SSO) hostis electric multipolar interaction. Sr 2 SiO 4 (SSO):Tb 3+ , Ce 3+ phosphor exhibits good thermal stability, the quantum yield wasabout 43.67%, indicating a potential candidate for solid-state lighting.

Prediction of Screw Loosening After Dynamic Pedicle Screw Fixation With Lumbar Polyetheretherketone Rods Using Magnetic Resonance Imaging-Based Vertebral Bone Quality Score

Guozheng Jiang,Luchun Xu,Yukun Ma,Jianbin Guan,Yongdong Yang,Wenqing Zhong,Wenhao Li,Shibo Zhou,JiaWei Song,Ningning Feng,Ziye Qiu,Zeyu Li,YiShu Zhou,Letian Meng,Yi Qu,Xing Yu 대한척추신경외과학회 2024 Neurospine Vol.21 No.2

Objective: To investigate the correlation between magnetic resonance imaging-based vertebral bone quality (VBQ) score and screw loosening after dynamic pedicle screw fixation with polyetheretherketone (PEEK) rods, and evaluate its predictive value. Methods: A retrospective analysis was conducted on the patients who underwent dynamic pedicle screw fixation with PEEK rods from March 2017 to June 2022. Data on age, sex, body mass index, hypertension, diabetes, hyperlipidemia history, long-term smoking, alcohol consumption, VBQ score, L1–4 average Hounsfield unit (HU) value, surgical fixation length, and the lowest instrumented vertebra were collected. Logistic regression analysis was employed to assess the relationship between VBQ score and pedicle screw loosening (PSL). Results: A total of 24 patients experienced PSL after surgery (20.5%). PSL group and nonPSL group showed statistical differences in age, number of fixed segments, fixation to the sacrum, L1–4 average HU value, and VBQ score (p < 0.05). The VBQ score in the PSL group was higher than that in the non-PSL group (3.56 ± 0.45 vs. 2.77 ± 0.31, p < 0.001). In logistic regression analysis, VBQ score (odds ratio, 3.425; 95% confidence interval, 1.552–8.279) were identified as independent risk factors for screw loosening. The area under the receiver operating characteristic curve for VBQ score predicting PSL was 0.819 (p < 0.05), with the optimal threshold of 3.15 (sensitivity, 83.1%; specificity, 80.5%). Conclusion: The VBQ score can independently predict postoperative screw loosening in patients undergoing lumbar dynamic pedicle screw fixation with PEEK rods, and its predictive value is comparable to HU value.