Numerical studies of the suppression of vortex-induced vibrations of twin box girders by central grids

Li, Zhiguo,Zhou, Qiang,Liao, Haili,Ma, Cunming Techno-Press 2018 Wind and Structures, An International Journal (WAS Vol.26 No.5

A numerical study based on a delayed detached eddy simulation (DDES) is conducted to investigate the aerodynamic mechanism behind the suppression of vortex-induced vibrations (VIVs) of twin box girders by central grids, which have an inhibition effect on VIVs, as evidenced by the results of section model wind tunnel tests. The mean aerodynamic force coefficients with different attack angles are compared with experimental results to validate the numerical method. Next, the flow structures around the deck and the aerodynamic forces on the deck are analyzed to enhance the understanding of the occurrence of VIVs and the suppression of VIVs by the application of central grids. The results show that shear layers are separated from the upper railings and lower overhaul track of the upstream girder and induce large-scale vortices in the gap that cause periodical lift forces of large amplitude acting on the downstream girder, resulting in VIVs of the bridge deck. However, the VIVs are apparently suppressed by the central grids because the vortices in the central gap are reduced into smaller vortices and become weaker, causing slightly fluctuating lift forces on the deck. In addition, the mean lift force on the deck is mainly caused by the upstream girder, whereas the fluctuating lift force is mainly caused by the downstream girder.

Coprinus Comatus-Based Nitrogen-Doped Active Carbon for High Performance Supercapacitor

Guofu Ma,Wei Tang,Kanjun Sun,Zhiguo Zhang,Enke Feng,Ziqiang Lei 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.8

Coprinus comatus-based nitrogen-doped activated carbon (N-ACC) is prepared by chemical activation and nitrogen-doped methods. The N-ACC possesses large specific surface areas (976.96m2 g -1), high nitrogen contents (11.53 wt.%), and super hydrophilicity. As electrode material for supercapacitors, the N-ACC shows remarkable electrochemical performance, such as 346 F g -1 maximum specific capacitance at a current density of 1A g -1, which retains 260 F g -1 even at a high current density of 10 A g -1 (about 75% capacitance retention) in 2MKOH aqueous electrolyte. The assembled N-ACC//N-ACC symmetric supercapacitor exhibits energy density of 14.63 Wh kg -1 at power density of 810 W kg -1, and excellent cycling stability with 92% specific capacitance retention after 10000 cycles in the voltage range 0–1.8V in 0.5M Na2SO4 aqueous solution. These results indicate that the N-ACC as electrode materials can be used for high performance supercapacitors.

Wind-induced vibrations and suppression measures of the Hong Kong-Zhuhai-Macao Bridge

Cunming Ma,Zhiguo Li,Fanchao Meng,Haili Liao,Junxin Wang 한국풍공학회 2021 Wind and Structures, An International Journal (WAS Vol.32 No.3

A series of wind tunnel tests, including 1:50 sectional model tests, 1:50 free-standing bridge tower tests and 1:70 full-bridge aeroelastic model tests were carried out to systematically investigate the aerodynamic performance of the Hong Kong-Zhuhai-Macao Bridge (HZMB). The test result indicates that there are three wind-resistant safety issues the HZMB encounters, including unacceptable low flutter critical wind speed, vertical vortex-induced vibration (VIV) of the main girder and galloping of the bridge tower in across-wind direction. Wind-induced vibration of HZMB can be effectively suppressed by the application of aerodynamic and mechanical measures. Acceptable flutter critical wind speed is achieved by optimizing the main girder form (before: large cantilever steel box girder, after: streamlined steel box girder) and cable type (before: central cable, after: double cable); The installations of wind fairing, guide plates and increasing structural damping are proved to be useful in suppressing the VIV of the HZMB; The galloping can be effectively suppressed by optimizing the interior angle on the windward side of the bridge tower. The present works provide scientific basis and guidance for wind resistance design of the HZMB.

The delamination of carbon fiber reinforced composites during cutting by flexible linear shaped charge

Jing Sun,Zhiguo Ma,Zhifeng Zhang,Fei Weng,Rong Chen 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.4

The delamination is a typical phenomenon when the carbon fiber reinforced composites (CFRC) undergoes blasting impact loading and the delamination will reduce both the strength and stiffness of the laminates, which can lead to catastrophic consequences while used as rocket skin. In this paper, the response of CFRC laminate is cut by flexible linear shaped charge (FLSC) and the delamination behavior of the CFRC is analyzed and discussed. The displacement interferometer system for any reflector (DISAR) is used to monitor the velocity of characteristic points of the laminate subjected to FLSC. Finite element analysis has been conducted to explain the mechanisms of delamination. Based on the numerical simulation, the influences of structural design parameters on the delamination effect of the CFRC after cutting are investigated. The results show that a large number of debris are produced at the center of the explosion and a small amount of large debris is produced at weakening groove on both sides. The delamination effect is greatly affected by the inter-laminar tensile strength and thickness of composite laminate, but it is not significantly affected by the linear density of the FLSC and stand-off.

Microbial short-chain fatty acids: a bridge between dietary fibers and poultry gut health — A review

Ali Qasim,Ma Sen,La Shaokai,Guo Zhiguo,Liu Boshuai,Gao Zimin,Farooq Umar,Wang Zhichang,Zhu Xiaoyan,Cui Yalei,Li Defeng,Shi Yinghua 아세아·태평양축산학회 2022 Animal Bioscience Vol.35 No.10

The maintenance of poultry gut health is complex depending on the intricate balance among diet, the commensal microbiota, and the mucosa, including the gut epithelium and the superimposing mucus layer. Changes in microflora composition and abundance can confer beneficial or detrimental effects on fowl. Antibiotics have devastating impacts on altering the landscape of gut microbiota, which further leads to antibiotic resistance or spread the pathogenic populations. By eliciting the landscape of gut microbiota, strategies should be made to break down the regulatory signals of pathogenic bacteria. The optional strategy of conferring dietary fibers (DFs) can be used to counterbalance the gut microbiota. DFs are the non-starch carbohydrates indigestible by host endogenous enzymes but can be fermented by symbiotic microbiota to produce shortchain fatty acids (SCFAs). This is one of the primary modes through which the gut microbiota interacts and communicate with the host. The majority of SCFAs are produced in the large intestine (particularly in the caecum), where they are taken up by the enterocytes or transported through portal vein circulation into the bloodstream. Recent shreds of evidence have elucidated that SCFAs affect the gut and modulate the tissues and organs either by activating G-protein-coupled receptors or affecting epigenetic modifications in the genome through inducing histone acetylase activities and inhibiting histone deacetylases. Thus, in this way, SCFAs vastly influence poultry health by promoting energy regulation, mucosal integrity, immune homeostasis, and immune maturation. In this review article, we will focus on DFs, which directly interact with gut microbes and lead to the production of SCFAs. Further, we will discuss the current molecular mechanisms of how SCFAs are generated, transported, and modulated the pro-and anti-inflammatory immune responses against pathogens and host physiology and gut health. The maintenance of poultry gut health is complex depending on the intricate balance among diet, the commensal microbiota, and the mucosa, including the gut epithelium and the superimposing mucus layer. Changes in microflora composition and abundance can confer beneficial or detrimental effects on fowl. Antibiotics have devastating impacts on altering the landscape of gut microbiota, which further leads to antibiotic resistance or spread the pathogenic populations. By eliciting the landscape of gut microbiota, strategies should be made to break down the regulatory signals of pathogenic bacteria. The optional strategy of conferring dietary fibers (DFs) can be used to counterbalance the gut microbiota. DFs are the non-starch carbohydrates indigestible by host endogenous enzymes but can be fermented by symbiotic microbiota to produce shortchain fatty acids (SCFAs). This is one of the primary modes through which the gut microbiota interacts and communicate with the host. The majority of SCFAs are produced in the large intestine (particularly in the caecum), where they are taken up by the enterocytes or transported through portal vein circulation into the bloodstream. Recent shreds of evidence have elucidated that SCFAs affect the gut and modulate the tissues and organs either by activating G-protein-coupled receptors or affecting epigenetic modifications in the genome through inducing histone acetylase activities and inhibiting histone deacetylases. Thus, in this way, SCFAs vastly influence poultry health by promoting energy regulation, mucosal integrity, immune homeostasis, and immune maturation. In this review article, we will focus on DFs, which directly interact with gut microbes and lead to the production of SCFAs. Further, we will discuss the current molecular mechanisms of how SCFAs are generated, transported, and modulated the pro-and anti-inflammatory immune responses against pathogens and host physiology and gut health.

NEW RESEARCH AND DEVELOPMENT IN VIBRATION UTILIZATION ENGINEERING

Wen Bangchun,Li Yinong,Yan Shirong,Ma Zhiguo,Han Qinkai,Zhang Hong 한국소음진동공학회 1997 한국소음진동공학회 국제학술대회논문집 Vol.1997 No.1

New Research and Development in Vibration Utilization Engineering

Bang Chun Wen,Yi Nong Li,Shirong Yan,Zhiguo Ma,Qinkai Han,Hong Zhang 대한기계학회 1997 Asia-Pacific Vibration Conference Vol.1 No.1