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Hydrodynamics of A Flexible Riser Undergoing the Vortex-Induced Vibration at High Reynolds Number

China Ocean Engineering 2018年第5期32卷 570-581页

作者： REN Tie ZHANG meng-meng FU Shi-xiao SONG lei-jian State Key Laboratory of Ocean Engineering Shanghai Jiao Tong UniversityShanghai 200240China Collaborative Innovation Centre for Advanced Ship and Deep-Sea Exploration Shanghai 200240China Marine Design&Research Institute of China Shanghai 200011China Shanghai Electric Wind Power Group Shanghai 200030China

This study proposed a method to obtain hydrodynamic forces and coefficients for a flexible riser undergoing the vortex-induced vibration(VIV), based on the measured strains collected from the scale-model testing with the Reynolds numbers ranging from 1.34 E5 to 2.35 E5. The riser is approximated as a tensioned spatial beam, and an inverse method based on the FEM of spatial beam is adopted for the calculation of hydrodynamic forces in the cross flow(CF) and inline(IL) directions. The drag coefficients and vortex-induced force coefficients are obtained through the Fourier Series Theory. Finally, the hydrodynamic characteristics of a flexible riser model undergoing the VIV in a uniform flow are carefully investigated. The results indicate that the VIV amplifies the drag coefficient, and the drag coefficient does not change with time when the CF VIV is stable. Only when the VIVs in the CF and IL directions are all steady vibrations, the vortex-induced force coefficients keep as a constant with time, and under"lock-in" condition, whether the added-mass coefficient changes with time or not, the oscillation frequency of the VIV keeps unchanged. It further shows that the CF excitation coefficients at high frequency are much smaller than those at the dominant frequency, while, the IL excitation coefficients are in the same range. The axial distributions of the excitation and damping region at the dominant frequency and high frequency are approximately consistent in the CF direction, while, in the IL direction, there exists a great difference.

关键词： flexible riser vortex-induced vibration vortex-induced force excitation coefficient added-mass coefficient drag coefficient

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AlN precipitation during steel solidification using CA model

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Journal of Iron and Steel Research International 2022年第11期29卷 1789-1799页

作者： lei Cui Yi-han Shi Xiang-ning meng Key Laboratory for Ecological Metallurgy of Multi-Metallic Ores Northeastern UniversityShenyang 110819LiaoningChina School of Metallurgy Northeastern UniversityShenyang 110819LiaoningChina

Based on the principles of metal solidification and cellular automaton(CA),as well as AlN precipitation thermodynamics and kinetics,a CA model of interdendritic AlN precipitation was established by coupling a large-size mesh describing the dendrite growth of Fe-C-Al-N alloys and a small-size mesh representing AlN precipitation based on transient chemical *** results of single dendrite growth stimulated by this model were compared with the Lipton-Glicksman-Kurz solution to verify the correctness of the matrix dendrite growth *** AlN morphology and dimensions obtained from the CA model simulations are following the experimental *** presence of equiaxed dendrite in the computational domain results in a significant coarsening of the columnar dendrite and a uniform solute distribution around them,and the AlN solid phase fraction *** of AlN precipitation at different wetting angles were also performed,and it was found that the solid phase fraction of AlN decreased with the increase in wetting ***,it is confirmed that the established model is an effective method to simulate interdendritic AlN precipitation.

关键词： Metal solidification Cellular automaton Wetting angle AlN precipitation Dendrite growth

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Energy Saving for Automatic Train Control in Moving Block Signaling System

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China Communications 2014年第A2期11卷 12-22页

作者： GU qing meng Yu MA Fei School of Mechanical Engineering University of Science and Technology Beijing Beijing 100083 E R. China

With rapid development of the railway traffic, the moving block signaling system （MBS） method has become more and more important for increasing the track capacity by allowing trains to run in a shorter time-headway while maintaining the required safety margins. In this framework, the tracking target point of the following train is moving forward with its leading train. This paper focuses on the energy saving tracking control of two successive trains in MBS. Nonlinear programming method is used to optimize the energy-saving speed trajectory of the following train. The real-time location of the leading train could be integrated into the optimization process. Due to simplicity, it can be used for online implementation. The feasibility and effectiveness are verified through simulation. The results show that the new method is efficient on energy saving even when disturbances present.

关键词： moving block signaling (MBS) energy saving automatic train protection (ATP) automatic train operation (ATO) tracking train speed trajectory

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A step deformation method for superplasticity improvement of coarse-grained Ti–15V–3Cr-3Sn-3Al

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Chinese Journal of Aeronautics 2018年第7期31卷 1619-1624页

作者： Cheng-Hong ZOU qing ZHOU lei WANG College of Mechanical and Electrical Engineering Nanjing University of Aeronautics and Astronautics

Ti–15V–3Cr–3Sn–3Al（Ti–15–3）, a kind of metastable beta titanium which has high specific strength and good cold-formability, is highlighted for applications in the aerospace manufacture industry. However, the technique for improving its formability at elevated temperatures is still a challenge at present. In this work, a step deformation method is proposed for superplasticity improvement of coarse grained Ti–15–3 plates at temperatures around its beta transus. The effects of the strain rate and the strain at the first stage on the superplasticity are investigated. The results show an increase of the strain rate sensitivity and a decrease of the flow stress under the step deformation mode compared to those obtained under constant strain rates at 780℃. The maximum strain to failure obtained in the step mode is 93% higher than that deformed in the constant strain rate mode. Strain rates, strains at the first stage, and temperatures have influences on the superplasticity improvement. The deformation mechanism is concluded as subgrain formation accommodated by grain boundary sliding rate-controlled by dislocation climb. The improved m value in the step deformation is accounted to the extra dislocation density produced during the strain rate reduction.

关键词： Dynamic recrystatlization Strain rate sensitivity Subgrain Superplasticity Titanium alloy

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Highly band-selective meta-surfaces exhibiting perfect near infrared absorption and concurrent visible band sensing:A numerical study

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Science China(Technological Sciences) 2022年第4期65卷 809-816页

作者： lei ZhiJie QIAN XiaoShi JIANG Kun meng Guang Interdisciplinary Research Center for Engineering Science School of Mechanical EngineeringShanghai Jiao Tong UniversityShanghai 200240China

We report a highly band-selective,bifunctional meta-surface that serves as an ultra-wide perfect absorber for near-infrared(NIR)band and a visible-band sensor,based on a rational design strategy involving stacking and/or grating of metals,inorganic insulators,and stimuli-responsive ***-based hydrogel was utilized as a layer of stimuli-responsive insulator,which is allowed to reversibly swell and collapse in one dimension in response to stimuli such as ambient temperature and chemical environment to empower the sensing capability in the visible band,with the perfect absorption in NIR region *** average absorption reached an impressive 99.4%from 780 to 2500 nm,which is attributed to the synergy of localized surface plasmon(LSP),propagating surface plasmon(PSP),and cavity *** reported bi-functional meta-surface is particularly attractive for band-selective solar energy harvesting,naked-eye sensing,and adaptive imaging.

关键词： hydrogel meta-surfaces absorber sensor

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A novel three-inflection-point sliding mode control framework for forward-tilting morphing aerospace vehicle with performance constraints and actuator faults

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Chinese Journal of Aeronautics 2024年第8期37卷 293-310页

作者： Xinkai LI lei DOU Hongli ZHANG Yue meng School of Electrical Engineering Xinjiang UniversityUrumqi 830047China

A prescribed performance control scheme based on the three-inflection-point hyperbolic function and predefined time performance function is proposed to solve the trajectory tracking problem of the forward-tilting morphing aerospace vehicle with time-varying actuator *** accurately estimate the loss degree of actuator faults,an immersion and invariance observer based on the predefined time dynamic scale factor is designed to estimate and compensate it.A composite dynamic sliding mode surface is designed using a three-inflection-point hyperbolic function,and a novel three-inflection-point sliding mode control framework is *** convergent domain of the sliding manifold is adjusted by parameters,and the system error convergence is controllable.A transfer function is designed to eliminate the sensitivity of the three-inflection-point hyperbolic sliding mode to the unknown initial state,and combined with the barrier Lyapunov function,and the performance constraint of the system is *** global asymptotic stability of the system is demonstrated using a strict mathematical *** effectiveness and superiority of the proposed control scheme are proven by simulation experiments.

关键词： Morphing aerospace vehicle Actuator faults Immersion and invariance Three-inflection-point sliding mode control Prescribed performance control

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A simple construction of CRT-based ideal secret sharing scheme and its security extension based on common factor

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Frontiers of Computer Science 2022年第1期16卷 155-163页

作者： lei WU Fuyou MIAO Keju meng Xu WANG School of Computer Science and Technology University of Science and Technology of ChinaHefei230026China

Secret sharing(SS)is part of the essential techniques in cryptography but still faces many challenges in efficiency and ***,SS schemes based on the Chinese Remainder Theorem(CRT)are either low in the information rate or complicated in *** solve the above problems,1)a simple construction of an ideal(t,n)-SS scheme is proposed based on CRT for a polynomial *** with Ning’s scheme,it is much more efficient in generating n pairwise coprime modular polynomials during the scheme construction ***,Shamir’s scheme is also a special case of our *** further improve the security,2)a common-factor-based(t,n)-SS scheme is proposed in which all shareholders share a common polynomial *** enables both the verification of received shares and the establishment of a secure channel among shareholders during the reconstruction *** a result,the scheme is resistant to eavesdropping and modification attacks by outside adversaries.

关键词： ideal secret sharing Chinese remainder theorem coprime polynomial generation common factor

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A variational formula for controlled backward stochastic partial differential equations and some application

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Applied Mathematics(A Journal of Chinese Universities) 2014年第3期29卷 295-306页

作者： meng qing-xin TANG Mao-ning Department of Mathematics Huzhou Teachers College School of Mathematical Sciences Fudan University

An optimal control problem for a controlled backward stochastic partial differential equation in the abstract evolution form with a Bolza type performance functional is considered. The control domain is not assumed to be convex, and all coefficients of the system are allowed to be random. A variational formula for the functional in a given control process direction is derived, by the Hamiltonian and associated adjoint system. As an application, a global stochastic maximum principle of Pontraygins type for the optimal controls is established.

关键词： Variational formula stochastic evolution equation backward stochastic evolution equation,stochastic maximum principle spike variation.

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Effect of Strain Ratio on Fatigue Model of Ultra-fine Grained Pure Titanium

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Journal of Wuhan University of Technology(Materials Science) 2023年第5期38卷 1169-1178页

作者： QIANG meng YANG Xirong LIU Xiaoyan LUO lei Wuhan Institute of Marine Electric Propulsion Wuhan 430064China

The ultra-fine grained(UFG)pure titanium was prepared by equal channel angular pressing(ECAP)and rotary swaging(RS).The strain controlled low cycle fatigue(LCF)test was carried out at room *** fatigue life prediction model and mean stress relaxation model under asymmetrical stress load were *** results show that the strain ratio has a significant effect on the low cycle fatigue performance of the UFG pure titanium,and the traditional Manson-coffin model can not accurately predict the fatigue life under asymmetric stress ***,the SWT mean stress correction model and three-parameter power curve model are proposed,and the test results are *** final research shows that the threeparameter power surface model has better *** studying the mean stress relaxation phenomenon under the condition of R≠-1,it is revealed that the stress ratio and the strain amplitude are the factors that significantly afiect the mean stress relaxation rate,and the mean stress relaxation model with the two variables is calculated to describe the mean stress relaxation phenomenon of the UFG pure titanium under different strain *** fracture morphology of the samples was observed by SEM,and it was concluded that the final fracture zone of the fatigue fracture of the UFG pure titanium was a mixture of ductile fracture and quasi cleavage *** toughness of the material increases with the increase of strain ratio at the same strain amplitude.

关键词： ultra-fine grained pure titanium low cycle fatigue life model mean stress relaxation mode strain ratio fracture morphology

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Feature Relationships Learning Incorporated Age Estimation Assisted by Cumulative Attribute Encoding

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Computers, Materials & Continua 2018年第9期56卷 467-482页

作者： qing Tian meng Cao Tinghuai Ma School of Computer and Software Nanjing University of Information Science and TechnologyNanjing210044China Jiangsu Engineering Center of Network Monitoring Nanjing University of Information Science and TechnologyNanjing210044China School of Electrical and Electronic Engineering University of ManchesterManchesterM139PLUK

The research of human facial age estimation(AE)has attracted increasing attention for its wide *** to date,a number of models have been constructed or employed to perform *** the goal of AE can be achieved by either classification or regression,the latter based methods generally yield more promising results because the continuity and gradualness of human aging can naturally be preserved in age ***,the neighbor-similarity and ordinality of age labels are not taken into account *** overcome this issue,the cumulative attribute(CA)coding was *** such age label relationships can be parameterized via CA coding,the potential relationships behind age features are not incorporated to estimate *** this end,in this paper we propose to perform AE by encoding the potential age feature relationships with CA coding via an implicit modeling *** that,we further extend our model to gender-aware AE by taking into account gender variance in aging ***,we experimentally validate the superiority of the proposed methodology.

关键词： Age estimation cumulative attribute gender-aware age estimation correlation relationship learning

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