A novel WOA-based structural damage identification using weighted modal data and flexibility assurance criterion

Zexiang Chen,Ling Yu 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.4

Structural damage identification (SDI) is a crucial step in structural health monitoring. However, some of the existing SDI methods cannot provide enough identification accuracy and efficiency in practice. A novel whale optimization algorithm (WOA) based method is proposed for SDI by weighting modal data and flexibility assurance criterion in this study. At first, the SDI problem is mathematically converted into a constrained optimization problem. Unlike traditional objective function defined using frequencies and mode shapes, a new objective function on the SDI problem is formulated by weighting both modal data and flexibility assurance criterion. Then, the WOA method, due to its good performance of fast convergence and global searching ability, is adopted to provide an accurate solution to the SDI problem, different predator mechanisms are formulated and their probability thresholds are selected. Finally, the performance of the proposed method is assessed by numerical simulations on a simply-supported beam and a 31-bar truss structures. For the given multiple structural damage conditions under environmental noises, the WOA-based SDI method can effectively locate structural damages and accurately estimate severities of damages. Compared with other optimization methods, such as particle swarm optimization and dragonfly algorithm, the proposed WOA-based method outperforms in accuracy and efficiency, which can provide a more effective and potential tool for the SDI problem.

Ballistic electronic and thermal conductance of monolayer and bilayer black phosphorus

Zexiang Deng,Huanjun Chen,Zhibing Li,Weiliang Wang 한국물리학회 2017 Current Applied Physics Vol.17 No.2

We performed first principle calculations based on density functional theory and GW approximation with Landauer approach to study ballistic electronic conductance and ballistic thermal conductance of black phosphorus (BP) whose dimensions are smaller than the mean free path of carriers. Ballistic electronic conductance of monolayer BP and bilayer BP with four different stacking styles, and ballistic thermal conductance of monolayer BP were investigated. The electronic transmission value along armchair direction is found to be a little higher than that along zigzag direction near the band gap energy range. Our calculations showed that, the G point hole effective mass along zigzag direction is stackingstyle sensitive, while other G point effective mass is independent of stacking style. We also reported the anisotropic ballistic thermal conductance of monolayer BP: the anisotropic ballistic thermal conductance ratio of zigzag-to-armchair approaches a constant (about 2.0) when the temperature is beyond 200 K. The reasons for these properties were discussed.

Modeling, analysis and experimental verification of two non‑electrolytic capacitor Z‑source converters

Guidong Zhang,Zexiang Chen,Samson S. Yu 전력전자학회 2023 JOURNAL OF POWER ELECTRONICS Vol.23 No.3

This paper gives a detailed theoretical analysis of two popular non-electrolytic capacitor NEC–Z-source converters (NEC– ZSCs) including analyses of their operation, the voltage stresses of the capacitors and diodes, the current stresses of the inductors, the voltage and current stresses of the switches, and the voltage gain with and without considering parasitic parameters. Parameter design and small signal modeling of NEC–ZSCs are conducted, and a proportional–integral (PI) controller is designed to form the closed-loop control circuit. Simulations and experiments are conducted and their results are collected and analyzed. These results corroborate the feasibility and effectiveness of the theoretical analysis for the two NEC–ZSCs and the closed-loop control design.

CFD study on hydraulic performance of subsurface flow constructed wetland: Effect of distribution and catchment area

Liwei Fan,Reti Hai,Zexiang Lu 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.5

A subsurface flow constructed wetland (SSFW) was simulated by using a commercial computational fluid dynamic (CFD) code (Fluent 6.22, Fluent Inc.). The liquid residence time distribution in the SSFW was obtained by the particle trajectory model. The simulation confirmed that the effect of the distribution and/or catchment area on the hydraulic efficiency is significant. An inappropriate horizontal distribution and/or catchment area can result in poor hydraulic efficiency. The hydraulic efficiency of the SSFW with the vertical distribution and/or catchment area can be kept at a high level (above 0.898). The design of the vertical distribution and/or catchment area in the SSFW is better than that of the horizontal. From the point of view of the engineering design, a small dimension distribution and/or catchment area in the SSFW is advisable, which maintains a considerable hydraulic efficiency of the SSFW (above 0.840), but also benefits the increase of the purge area.

Multi-strategy structural damage detection based on included angle of vectors and sparse regularization

Huan-Lin Liu,Ling Yu,Ziwei Luo,Zexiang Chen 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.4

Recently, many structural damage detection (SDD) methods have been proposed to monitor the safety of structures. As an important modal parameter, mode shape has been widely used in SDD, and the difference of vectors was adopted based on sensitivity analysis and mode shapes in the existing studies. However, amplitudes of mode shapes in different measured points are relative values. Therefore, the difference of mode shapes will be influenced by their amplitudes, and the SDD results may be inaccurate. Focus on this deficiency, a multi-strategy SDD method is proposed based on the included angle of vectors and sparse regularization in this study. Firstly, inspired by modal assurance criterion (MAC), a relationship between mode shapes and changes in damage coefficients is established based on the included angle of vectors. Then, frequencies are introduced for multi-strategy SDD by a weighted coefficient. Meanwhile, sparse regularization is applied to improve the ill-posedness of the SDD problem. As a result, a novel convex optimization problem is proposed for effective SDD. To evaluate the effectiveness of the proposed method, numerical simulations in a planar truss and experimental studies in a six-story aluminum alloy frame in laboratory are conducted. The identified results indicate that the proposed method can effectively reduce the influence of noises, and it has good ability in locating structural damages and quantifying damage degrees.

Anti-sparse representation for structural model updating using l∞ norm regularization

Ziwei Luo,Ling Yu,Huan-Lin Liu,Zexiang Chen 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.4

Finite element (FE) model based structural damage detection (SDD) methods play vital roles in effectively locating and quantifying structural damages. Among these methods, structural model updating should be conducted before SDD to obtain benchmark models of real structures. However, the characteristics of updating parameters are not reasonably considered in existing studies. Inspired by the l∞ norm regularization, a novel anti-sparse representation method is proposed for structural model updating in this study. Based on sensitivity analysis, both frequencies and mode shapes are used to define an objective function at first. Then, by adding l∞ norm penalty, an optimization problem is established for structural model updating. As a result, the optimization problem can be solved by the fast iterative shrinkage thresholding algorithm (FISTA). Moreover, comparative studies with classical regularization strategy, i.e. the l2 norm regularization method, are conducted as well. To intuitively illustrate the effectiveness of the proposed method, a 2-DOF spring-mass model is taken as an example in numerical simulations. The updating results show that the proposed method has a good robustness to measurement noises. Finally, to further verify the applicability of the proposed method, a six-storey aluminum alloy frame is designed and fabricated in laboratory. The added mass on each storey is taken as updating parameter. The updating results provide a good agreement with the true values, which indicates that the proposed method can effectively update the model parameters with a high accuracy.

Plasmonic and passivation effects of Au decorated RGO@CdSe nanofilm uplifted by CdSe@ZnO nanorods with photoelectrochemical enhancement

Zhang, Zhuo,Choi, Mingi,Baek, Minki,Deng, Zexiang,Yong, Kijung Elsevier 2016 Nano energy Vol.21 No.-

<P><B>Abstract</B></P> <P>Here, we demonstrate that the photoactivity of gold (Au)-decorated two-story hetero-nanostructures for photoelectrochemical (PEC) efficiency can be effectively enhanced by the plasmonic effect between Au and semiconductors in the visible region and by the passivation effect in the UV region. An Au-decorated two-story hetero-nanostructure was prepared as follows. The upper story is a novel hetero-nanofilm consisting of a reduced graphene oxide (RGO) nanofilm covered by a large area of crystalline CdSe nanolayer with a (111) plane outside and a thickness less than 8nm; the bottom story consists of CdSe-coated ZnO hetero-nanorods. In the visible region, the plasmonic effects between Au and other materials, such as ZnO, CdSe and RGO, were analyzed separately by reassembling the component ZnO nanorods, the CdSe layer and the RGO nanofilm. The photoconversion of the two-story hetero-nanostructure can be improved via the plasmonic effects between Au and n-type semiconductors, such as ZnO and CdSe, due to the stronger Schottky rectifier effects and hot-electron injection. In the UV light region, the photoconversion can be dramatically enhanced via the passivation of surface trap states. Moreover, the electron lifetime of the two-story hetero-nanostructure can also be improved by the suppression of electron–hole recombination by the Au nanoparticles and RGO nanofilms. Overall, CdSe-covered RGO hetero-nanofilms can increase the PEC efficiency 22.42 times over that of bare ZnO, while combination of the plasmonic and passivation effects can further improve this value by 20.7%, illustrating the potential of the two-story hetero-nanostructure in future photoelectrodes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The upper story is a hetero-nanofilm consisting of RGO covered by CdSe nanolayer less than 8 nm. </LI> <LI> The bottom story consists of CdSe-coated ZnO hetero-nanorods. </LI> <LI> In the visible region, photoconversion can be improved via plasmonic effects and Schottky contact. </LI> <LI> In the UV region, photoconversion can be enhanced via the passivation of surface trap states. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Corrosion-Assisted Self-Growth of Au-Decorated ZnO Corn Silks and Their Photoelectrochemical Enhancement

Zhang, Zhuo,Choi, Mingi,Baek, Minki,Deng, Zexiang,Yong, Kijung American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.4

<P>Modem nanotechnology generates more stringent requirements for the design and synthetic strategy of nanostructural materials. In this work, we demonstrate a novel strategy for the synthesis of 'corn silk'-like ZnO hierarchical nanostructures, simplified as ZnO corn silk: silk-like ZnO nanotubes (NTs) with a large length-to-diameter ratio are grown on the top tip of corn-shaped ZnO nanorods (NRs). The synthetic method is unique in that when the ZnO NRs are dipped into the aqueous solution of NaBH4, the release of Zn2+ and OH- caused by the corrosion of ZnO NRs, as well as the subsequent growth of, ZnO NTs, could allow the process to run step-by-step in self-assembly mode. This process is directed and driven by the change in concentrations of hydrogen anion H(s)(-) induced by NaBH4, as well as hydroxyl ions (OH-) induced by the H- formation and hydrolysis of dissociative Zn atoms. The prepared ZnO corn silks exhibit highly enhanced photoelectrochemical (PEC) efficiency after decoration with Au nanoparticles (NPs). ZnO silks act as pathways to facilitate efficient charge transfer, and the Au NP decoration induces the plasmonic effect, causing the hot electrons to inject into ZnO under visible illumination. At the same time, the formation of a Schottky barrier at the Au/ZnO interface can retard the electron-hole recombination. Overall, Au-decorated ZnO corn silk with an increased PEC efficiency represents a promising photoanode material, and the synthesis route developed in the current study is applicable to building hierarchical nanostructures of other materials.</P>

Thickness-dependent reversible hydrogenation of graphene layers.

Luo, Zhiqiang,Yu, Ting,Kim, Ki-Jeong,Ni, Zhenhua,You, Yumeng,Lim, Sanhua,Shen, Zexiang,Wang, Shanzhong,Lin, Jianyi American Chemical Society 2009 ACS NANO Vol.3 No.7

<P>In this work, graphene layers on SiO(2)/Si substrate have been chemically decorated by radio frequency hydrogen plasma. Hydrogen coverage investigation by Raman spectroscopy and micro-X-ray photoelectron spectroscopy characterization demonstrates that the hydrogenation of single layer graphene on SiO(2)/Si substrate is much less feasible than that of bilayer and multilayer graphene. Both the hydrogenation and dehydrogenation process of the graphene layers are controlled by the corresponding energy barriers, which show significant dependence on the number of layers. The extent of decorated carbon atoms in graphene layers can be manipulated reversibly up to the saturation coverage, which facilitates engineering of chemically decorated graphene with various functional groups via plasma techniques.</P>