针对牙买加当地大型起重设备租赁费用高且国内利用JQJ型(步履式)架桥机安装曲线半径200m、跨度超过40m的预制T梁较少的特点,文中结合牙买加Hagley Park Road道路改造工程200m超小曲线半径、40m预制T梁安装施工实践,总结了如何利用改装...针对牙买加当地大型起重设备租赁费用高且国内利用JQJ型(步履式)架桥机安装曲线半径200m、跨度超过40m的预制T梁较少的特点,文中结合牙买加Hagley Park Road道路改造工程200m超小曲线半径、40m预制T梁安装施工实践,总结了如何利用改装的双悬臂JQJ180型架桥机安装超小曲线半径预制T梁桥施工工艺,同时通过优化设计龙门吊吊具等措施,避免了曲线偏心梁起吊倾斜、不平稳的问题,解决了本项目重、难点问题,保证了主线桥顺利贯通,为其他类似工程提供一定的参考依据。展开更多
The present paper represents comparison of continuum shells and latticed shells with qualitative analysis. For shells, the mechanical characteristics in the two perpendicular directions are continuous and related to e...The present paper represents comparison of continuum shells and latticed shells with qualitative analysis. For shells, the mechanical characteristics in the two perpendicular directions are continuous and related to each other, and any change in thickness will result in change in stiffness in any direction. In latticed shells, members are discrete and stiffnesses in two mutually perpendicular directions are discontinuous and independent of each other. Therefore, sensitivity of geometrical imperfection for buckling of latticed shells should be different from that of continuum shells. The author proposes a shape optimization method for maximum buckling load of a latticed shell. A single layer latticed dome is taken as a numerical example, and the results show that the buckling load parameter for full area loading case increases 32.75% compared to that of its initial shape. Furthermore, the numerical example demonstrates that an optimum latticed shell with maximum buckling load, unlike an optimum continuum shell, may not be sensitive to its geometrical imperfection.展开更多
In this paper,we research general Defective Cion Problem under the model S,i.e,the number d of Defective cions is not fixed. For d=O,1,or 2. we get some good results.
Molybdenum disulfide（MoS2） has attracted extensive attention as an alternative to replace noble electrocatalysts in the hydrogen evolution reaction（HER）. Here, we highlight an efficient and straightforward ball mi...Molybdenum disulfide（MoS2） has attracted extensive attention as an alternative to replace noble electrocatalysts in the hydrogen evolution reaction（HER）. Here, we highlight an efficient and straightforward ball milling method,using nanoscale Cu powders as reductant to reduce MoS2 engineering S-vacancies into MoS2 surfaces, to fabricate a defectrich MoS2material（DR-MoS2）. The micron-sized DR-MoS2 catalysts exhibit significantly enhanced catalytic activity for HER with an overpotential（at 10 mA cm^-2） of 176 m V in acidic media and 189 m V in basic media, surpassing most of Mo-based catalysts previously reported, especially in basic solution. Meanwhile stability tests confirm the outstanding durability of DR-MoS2 catalysts in both acid and basic electrolytes. This work not only opens a new pathway to implant defects to MoS2, but also provides low-cost alternative for efficient electrocatalytic production of hydrogen in both alkaline and acidic environments.展开更多
According to previous studies,stiffened shells with convex hyperbolic generatrix shape are less sensitive to imperfections.In this study,the effects of generatrix shape on the performances of elastic and plastic buckl...According to previous studies,stiffened shells with convex hyperbolic generatrix shape are less sensitive to imperfections.In this study,the effects of generatrix shape on the performances of elastic and plastic buckling in stiffened shells are investigated.Then,a more general description of generatrix shape is proposed,which can simply be expressed as a convex B-spline curve(controlled by four key points).An optimization framework of stiffened shells with a convex B-spline generatrix is established,with optimization objective being measured in terms of nominal collapse load,which can be expressed as a weighted sum of geometrically imperfect shells.The effectiveness of the proposed framework is demonstrated by a detailed comparison of the optimum designs for the B-spline and hyperbolic generatrix shapes.The decrease of imperfection sensitivity allows for a significant weight saving,which is particularly important in the development of future heavy-lift launch vehicles.展开更多
To reduce the performance deterioration induced by imperfect channel state information(CSI) in correlated multiple input multiple output(MIMO) downlink,the linear transmit/receive filters should be optimized to be rob...To reduce the performance deterioration induced by imperfect channel state information(CSI) in correlated multiple input multiple output(MIMO) downlink,the linear transmit/receive filters should be optimized to be robust to imperfect CSI.A sub-optimization algorithm based on minimizing sum MSE conditional on available imperfect CSI estimates subject to a per-user power constraint is proposed.The algorithm adapts the existing MMSE algorithm from uncorrelated single-user MIMO system with perfect CSI to correlated MIMO downlink with imperfect CSI.Simulation shows that the suboptimal algorithm can effectively mitigate the performance loss induced by imperfect CSI and has a good convergence performance.In addition,the effect of spatial correlation on the performance of the proposed algorithm is also simulated.展开更多
This paper presents a node shift method to find the optimal distribution of nodes in single-layer reticulated shells. The optimization process searches for the minimum strain energy configuration and this leads to red...This paper presents a node shift method to find the optimal distribution of nodes in single-layer reticulated shells. The optimization process searches for the minimum strain energy configuration and this leads to reduced sensitivity in initial imper- fections. Strain energy sensitivity numbers are derived for free shift and restricted shift where nodes can move freely in the 3D space or have to move within a predefmed surface respectively. Numerical examples demonstrate the efficiency of the proposed approach. It was found that optimized structures achieve higher ultimate load and are less sensitive to imperfections than the initial structure. The configuration of the final structure is closely related to factors like the initial structural configuration, spatial conditions, etc. Based on different initial conditions, architects can be provided with diverse reasonable structures. Furthermore, by amending the defined shapes and nodal distributions, it is possible to improve the mechanical behavior of the structures.展开更多
文摘针对牙买加当地大型起重设备租赁费用高且国内利用JQJ型(步履式)架桥机安装曲线半径200m、跨度超过40m的预制T梁较少的特点,文中结合牙买加Hagley Park Road道路改造工程200m超小曲线半径、40m预制T梁安装施工实践,总结了如何利用改装的双悬臂JQJ180型架桥机安装超小曲线半径预制T梁桥施工工艺,同时通过优化设计龙门吊吊具等措施,避免了曲线偏心梁起吊倾斜、不平稳的问题,解决了本项目重、难点问题,保证了主线桥顺利贯通,为其他类似工程提供一定的参考依据。
文摘The present paper represents comparison of continuum shells and latticed shells with qualitative analysis. For shells, the mechanical characteristics in the two perpendicular directions are continuous and related to each other, and any change in thickness will result in change in stiffness in any direction. In latticed shells, members are discrete and stiffnesses in two mutually perpendicular directions are discontinuous and independent of each other. Therefore, sensitivity of geometrical imperfection for buckling of latticed shells should be different from that of continuum shells. The author proposes a shape optimization method for maximum buckling load of a latticed shell. A single layer latticed dome is taken as a numerical example, and the results show that the buckling load parameter for full area loading case increases 32.75% compared to that of its initial shape. Furthermore, the numerical example demonstrates that an optimum latticed shell with maximum buckling load, unlike an optimum continuum shell, may not be sensitive to its geometrical imperfection.
文摘In this paper,we research general Defective Cion Problem under the model S,i.e,the number d of Defective cions is not fixed. For d=O,1,or 2. we get some good results.
基金supported by the National Basic Research of China (2015CB932500 and 2013CB632702)the National Natural Science Fundation of China (51302141, 51501008, U1560103 and 61274015)
文摘Molybdenum disulfide（MoS2） has attracted extensive attention as an alternative to replace noble electrocatalysts in the hydrogen evolution reaction（HER）. Here, we highlight an efficient and straightforward ball milling method,using nanoscale Cu powders as reductant to reduce MoS2 engineering S-vacancies into MoS2 surfaces, to fabricate a defectrich MoS2material（DR-MoS2）. The micron-sized DR-MoS2 catalysts exhibit significantly enhanced catalytic activity for HER with an overpotential（at 10 mA cm^-2） of 176 m V in acidic media and 189 m V in basic media, surpassing most of Mo-based catalysts previously reported, especially in basic solution. Meanwhile stability tests confirm the outstanding durability of DR-MoS2 catalysts in both acid and basic electrolytes. This work not only opens a new pathway to implant defects to MoS2, but also provides low-cost alternative for efficient electrocatalytic production of hydrogen in both alkaline and acidic environments.
基金supported by the National Basic Research Program of China("973"Project)(Grant Nos.2014CB049000,2014CB046596)the National Natural Science Foundation of China(Grant Nos.11402049,11372062)+2 种基金the Project funded by China Postdoctoral Science Foundation(Grant No.2014M551070)the Fundamental Research Funds for Central University of China(Grant No.DUT14RC(3)028)the"111"Program(Grant No.B14013)
文摘According to previous studies,stiffened shells with convex hyperbolic generatrix shape are less sensitive to imperfections.In this study,the effects of generatrix shape on the performances of elastic and plastic buckling in stiffened shells are investigated.Then,a more general description of generatrix shape is proposed,which can simply be expressed as a convex B-spline curve(controlled by four key points).An optimization framework of stiffened shells with a convex B-spline generatrix is established,with optimization objective being measured in terms of nominal collapse load,which can be expressed as a weighted sum of geometrically imperfect shells.The effectiveness of the proposed framework is demonstrated by a detailed comparison of the optimum designs for the B-spline and hyperbolic generatrix shapes.The decrease of imperfection sensitivity allows for a significant weight saving,which is particularly important in the development of future heavy-lift launch vehicles.
基金the National Natural Science Foundationof China(No.60572156)
文摘To reduce the performance deterioration induced by imperfect channel state information(CSI) in correlated multiple input multiple output(MIMO) downlink,the linear transmit/receive filters should be optimized to be robust to imperfect CSI.A sub-optimization algorithm based on minimizing sum MSE conditional on available imperfect CSI estimates subject to a per-user power constraint is proposed.The algorithm adapts the existing MMSE algorithm from uncorrelated single-user MIMO system with perfect CSI to correlated MIMO downlink with imperfect CSI.Simulation shows that the suboptimal algorithm can effectively mitigate the performance loss induced by imperfect CSI and has a good convergence performance.In addition,the effect of spatial correlation on the performance of the proposed algorithm is also simulated.
基金Project supported by the National Natural Science Foundation of China （No. 50978075）
文摘This paper presents a node shift method to find the optimal distribution of nodes in single-layer reticulated shells. The optimization process searches for the minimum strain energy configuration and this leads to reduced sensitivity in initial imper- fections. Strain energy sensitivity numbers are derived for free shift and restricted shift where nodes can move freely in the 3D space or have to move within a predefmed surface respectively. Numerical examples demonstrate the efficiency of the proposed approach. It was found that optimized structures achieve higher ultimate load and are less sensitive to imperfections than the initial structure. The configuration of the final structure is closely related to factors like the initial structural configuration, spatial conditions, etc. Based on different initial conditions, architects can be provided with diverse reasonable structures. Furthermore, by amending the defined shapes and nodal distributions, it is possible to improve the mechanical behavior of the structures.
