Effects of longitudinal and transverse curvatures on optimal design of shell footbridge

Shiming Liu,Bin Huang,Yi Min Xie 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.80 No.1

Shell bridges have attracted extensive interest in engineering research and practice. This paper aims to evaluate the effects of longitudinal and transverse curvatures on the optimal design of the shell bridge. For this purpose, a slant-legged steel shell footbridge with the same initial and target volumes of steel was chosen to build parametric geometric models with different curvature radii, and then topology optimization was carried out using the bi-directional evolutionary structural optimization (BESO) technique to obtain optimized designs with high structural stiffness. Furthermore, linear static analysis and eigenvalue analysis demonstrate that the displacement, von Mises effective stress, and the first-order vertical vibration frequency satisfied all the requirements of design regulations. Numerical results indicate that not only the longitudinal curvature but also the transverse curvature have a significant effect on the optimized designs of steel shell footbridge. While the mean compliance increased with the transverse curvature radius, it first decreased and then increased with the longitudinal curvature radius.

Timoshenko beam-based stability and natural frequency analysis for heavy load mechanical spindles

Zhifeng Liu,Shiming Ma,Ligang Cai,Tieneng Guo,Yongsheng Zhao 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.11

The heavy load mechanical spindle is an important functional component in a 5-axis computer numerical control (CNC) machine tool,which is used to process large and complex free-form surfaces. It is necessary to obtain the natural frequency and analyze the spindle stability for improving the machining precision. In this paper, Timoshenko beam theory is introduced to model the mechanical spindle shaft, where the centrifugal force and gyroscopic effects are considered. Stability of the heavy load mechanical spindle shaft is analyzed,and the buckling load of the spindle shaft is obtained under different rotational speeds. The natural frequency of spindle is investigated in a freedom and restraint state, respectively. Comparing the proposed method with the simplified hollow cylinder and shaft prototype in the freedom state, the results show that they are highly correlated with experimental results. For the restraint state, the axial load, rotational speed, gyroscopic effect, and centrifugal force are discussed, and all of these parameters affect the natural frequency. The proposed modeling approach can be used for spindle design and optimization in a given machining process and can be easily extended to other spindle design.

A knowledge-based online fault detection method of the assembly process considering the relative poses of components

Yinhua Liu,Rui Sun,Yuwei Lu,Shiming Zhang 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.10

The real-time process fault detection in the multi-station assembly process is always a challenging problem for auto body manufactures. Traditionally, the fault diagnosis approaches for variation source identification are divided into two categories, i.e. the pattern matching methods and model-based estimation ones based on the collected data set. The measurements provide effective process monitoring, but the real-time process fault diagnosis in the assembly process is still difficult with the traditional diagnosis techniques, and always depends on the engineering experience in practice. Based on the assembly process knowledge, including multi-station assembly hierarchy, fixture scheme, measurement characteristics and tolerances etc. in the multi-station, a knowledge-based diagnostic methodology and procedures are proposed with the measurements of each body in white for part/component defections and faulty assembly station identification. For the station involved with defective parts/components, the sub-coordinate system of the part/component is established reflecting its position and pose in the space, and then the relative pose matrix to the “normally build” pose is calculated based on the deviations of sub-coordinates of the parts in this station. Finally, the assembly process malfunctions are determined by a proposed rule-based strategy with the relative pose matrix in real time. A simple 3 stations assembly process with 5 sheet metal parts was analyzed and compared with the traditional diagnostic method to verify the effectiveness and stability of the proposed method.

Analysis on the safe distance between shield tunnel through sand stratum and underlying karst cave

Wei Wan,Shiming Gao,Lingfeng Liu,Wushuang Wen,Ping Li,Jianping Chen 한국자원공학회 2019 Geosystem engineering Vol.22 No.2

When a subway tunnel passes through a karst geological area, in order to ensure the stability of the tunnel, the safe distance between the tunnel and karst cave needs to be researched. This article is based on the construction project of Wuhan metro line 6 from Qianjincun station to Mayinglu station. In view of the geological condition of overlying sand and underlying limestone, by using numerical simulation and theoretical calculation and selecting a characteristic section, the influence law and degree of karst cave span, height-span ratio, and filling degree on the safe thickness of karst cave roof are studied and a forecasting model of the safe thickness of karst cave roof is established. Combined with dichotomy and numerical simulation, the critical horizontal safe distance beyond which cave collapse does not cause tunnel instability is calculated. The results show that: (1) the safe thickness of karst cave roof increases linearly with the increase of karst cave span, and decreases with the increase of height-span ratio and filling degree; (2) among the three factors, the effect of karst cave span is the most significant, the filling degree of karst cave is the second, and the influence of height-span ratio of karst cave is the weakest; (3) the proposed forecasting model passes the significance test, indicating that the model is very reasonable; and (4) the critical horizontal safe distance from the tunnel border to the karst cave boundary is 22.4 m. The research results can provide guidance for the design and construction of shield tunnels and karst cave treatment in karst areas.

Effect of sintering temperature on properties of lightweightporous ceramics prepared by foam impregnation method

Zhili Cui,Shiming Xiao,Xianli Luo,Yunxuan Liu,Ming Liu,Yuyun Zeng,Xiaoli Zhong,Hong Zheng,Haifeng Guo 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.5

In this paper, cheap mineral materials were used as the base materials of lightweight porous ceramics prepared through foamimpregnation method. The effect of the sintering temperature on the properties of the prepared porous ceramics was studied. The porous ceramic was mainly composed of amorphous silicon oxide, crystalline cordierite and mullite phases, and a smallamount of alumina phase. As the sintering temperature increased, the porosity of porous ceramics gradually decreased from94% to 92%, and the bulk density increased from 0.173 gcm-3 at 1100 ℃ to 0.194 gcm-3 at 1200 ℃. The best sinteringtemperature was 1180 ℃. The porosity of the porous ceramics sintered at 1180 ℃ was 92.14%, the volume weight was 0.189gcm-3, the shrinkage rate was 15.80%, the compressive strength was 0.79 MPa, and the thermal conductivity was 0.295 Wm-1k-1. The lightweight porous ceramic has high porosity, low density and good thermal insulation, as well as low cost, having greatpotential for application in fields such as thermal insulation, adsorption, and environmental protection.

Deformation research of Silty Clay Under Freeze-Thaw Cycles

Lihui Tian,Liangliang Yu,Shiming Liu,Bo Zhang 대한토목학회 2020 KSCE Journal of Civil Engineering Vol.24 No.2

To explore the dynamic properties of silty clay in seasonally frozen ground under repeated freeze-thaw cycles, an unconsolidated undrained dynamic triaxial test was conducted on such properties under various confining pressures, number of freeze-thaw cycles, and dynamic stress amplitudes. The test results showed that due to the impact of freeze-thaw cycles, the inherent structure of the soil underwent some major changes, in which the resilient strain increased and the resilient modulus decreased. However, as the number of freeze-thaw cycles increased, the effect was reduced and eventually tended to be stable. As the number of freeze-thaw cycles increased, the cumulative plastic strain of the soil rose rapidly, and the soil samples became more prone to fracture at low stress amplitudes and small number of vibrations. The more the number of freeze-thaw cycles, the higher the cumulative plastic strain rate generated under a single dynamic stress amplitude. Moreover, with the increase in the confining pressure, the failure form of the thawed silty clay gradually evolved from a plastic fracture to a brittle one. The research results of this paper were helpful to further understand the influence of freeze-thaw cycle on the dynamic properties of silty clay, and provide data support for the subsequent research on the mechanism of roadbed diseases under the load in seasonally frozen ground.

De-cloaking Malicious Activities in Smartphones Using HTTP Flow Mining

( Xin Su ),( Xuchong Liu ),( Jiuchuang Lin ),( Shiming He ),( Zhangjie Fu ),( Wenjia Li ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.6

Android malware steals users` private information, and embedded unsafe advertisement (ad) libraries, which execute unsafe code causing damage to users. The majority of such traffic is HTTP and is mixed with other normal traffic, which makes the detection of malware and unsafe ad libraries a challenging problem. To address this problem, this work describes a novel HTTP traffic flow mining approach to detect and categorize Android malware and unsafe ad library. This work designed AndroCollector, which can automatically execute the Android application (app) and collect the network traffic traces. From these traces, this work extracts HTTP traffic features along three important dimensions: quantitative, timing, and semantic and use these features for characterizing malware and unsafe ad libraries. Based on these HTTP traffic features, this work describes a supervised classification scheme for detecting malware and unsafe ad libraries. In addition, to help network operators, this work describes a fine-grained categorization method by generating fingerprints from HTTP request methods for each malware family and unsafe ad libraries. This work evaluated the scheme using HTTP traffic traces collected from 10778 Android apps. The experimental results show that the scheme can detect malware with 97% accuracy and unsafe ad libraries with 95% accuracy when tested on the popular third-party Android markets.

Aligned nanofibrous collagen membranes from fish swim bladder as a tough and acid-resistant suture for pH-regulated stomach perforation and tendon rupture

Zhaohui Luan,Shuang Liu,Wei Wang,Kaige Xu,Shaosong Ye,Ruijue Dan,Hong Zhang,Zhenzhen Shu,Tongchuan Wang,Chaoqiang Fan,Malcolm Xing,Shiming Yang 한국생체재료학회 2022 생체재료학회지 Vol.26 No.4

Background: Wound closure in the complex body environment places higher requirements on suture’s mechanical and biological performance. In the scenario of frequent mechanical gastric motility and extremely low pH, single functional sutures have limitations in dealing with stomach bleeding trauma where the normal healing will get deteriorated in acid. It necessitates to advance suture, which can regulate wounds, resist acid and intelligently sense stomach pH. Methods: Based on fish swim bladder, a double-stranded drug-loaded suture was fabricated. Its cytotoxicity, histocompatibility, mechanical properties, acid resistance and multiple functions were verified. Also, suture’s performance suturing gastric wounds and Achilles tendon was verified in an in vivo model. Results: By investigating the swim bladder’s multi-scale structure, the aligned tough collagen fibrous membrane can resist high hydrostatic pressure. We report that the multi-functional sutures on the twisted and aligned collagen fibers have acid resistance and low tissue reaction. Working with an implantable “capsule robot”, the smart suture can inhibit gastric acid secretion, curb the prolonged stomach bleeding and monitor real-time pH changes in rabbits and pigs. The suture can promote stomach healing and is strong enough to stitch the fractured Achilles tendon. Conclusions: As a drug-loaded absorbable suture, the suture shows excellent performance and good application prospect in clinical work.

Cyano-Substituted Head-to-Head Polythiophenes: Enabling High-Performance n-Type Organic Thin-Film Transistors

Wang, Hang,Huang, Jun,Uddin, Mohammad Afsar,Liu, Bin,Chen, Peng,Shi, Shengbin,Tang, Yumin,Xing, Guichuan,Zhang, Shiming,Woo, Han Young,Guo, Han,Guo, Xugang American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.10

<P>Polythiophenes, built on the electron-rich thiophene unit, typically possess high-lying energy levels of the lowest unoccupied molecular orbitals (LUMOs) and show hole-transporting properties. In this study, we develop a series of n-type polythiophenes, <B>P1</B>-<B>P3</B>, based on head-to-head-linked 3,3′-dialkoxy-4,4′-dicyano-2,2′-bithiophene (BTCNOR) with distinct side chains. The BTCNOR unit shows not only highly planar backbone conformation enabled by the intramolecular noncovalent sulfur-oxygen interaction but also significantly suppressed LUMO level attributed to the cyano-substitution. Hence, all BTCNOR-based polymer semiconductors exhibit low-lying LUMO levels, which are ∼1.0 eV lower than that of regioregular poly(3-hexylthiophene) (rr-P3HT), a benchmark p-type polymer semiconductor. Consequently, all of the three polymers can enable unipolar n-type transport characteristics in organic thin-film transistors (OTFTs) with low off-currents (<I>I</I><SUB>off</SUB>s) of 10<SUP>-10</SUP>-10<SUP>-11</SUP> A and large current on/off ratios (<I>I</I><SUB>on</SUB>/<I>I</I><SUB>off</SUB>s) at the level of 10<SUP>6</SUP>. Among them, polymer <B>P2</B> with a 2-ethylhexyl side chain offers the highest film ordering, leading to the best device performance with an excellent electron mobility (μ<SUB>e</SUB>) of 0.31 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP> in off-center spin-cast OTFTs. To the best of our knowledge, this is the first report of n-type polythiophenes with electron mobility comparable to the hole mobility of the benchmark p-type rr-P3HT and approaching the electron mobility of the most-studied n-type polymer, poly(naphthalene diimide-<I>alt</I>-bithiophene) (i.e., N2200). The change of charge carrier polarity from p-type (rr-P3HT) to n-type (<B>P2</B>) with comparable mobility demonstrates the obvious effectiveness of our structural modification. Adoption of <I>n</I>-hexadecyl (<B>P1</B>) and 2-butyloctyl (<B>P3</B>) side chains leads to reduced film ordering and results in 1-2 orders of magnitude lower μ<SUB>e</SUB>s, showing the critical role of side chains in optimizing device performance. This study demonstrates the unique structural features of head-to-head linkage containing BTCNOR for constructing high-performance n-type polymers, i.e., the alkoxy chain for backbone conformation locking and providing polymer solubility as well as the strong electron-withdrawing cyano group for lowering LUMO levels and enabling n-type performance. The design strategy of BTCNOR-based polymers provides useful guidelines for developing n-type polythiophenes.</P> [FIG OMISSION]</BR>

Functionalized benzothieno[3,2 b]thiophenes (BTTs) for high performance organic thin-film transistors (OTFTs)

Youn, Jangdae,Huang, Peng-Yi,Zhang, Shiming,Liu, Chiao-Wei,Vegiraju, Sureshraju,Prabakaran, Kumaresan,Stern, Charlotte,Kim, Choongik,Chen, Ming-Chou,Facchetti, Antonio,Marks, Tobin J. The Royal Society of Chemistry 2014 Journal of materials chemistry. C, Materials for o Vol.2 No.36