An essential step for the realization of free-form surface structures is to create an efficient structural gird that satisfies not only the architectural aesthetics,but also the structural performance.Employing the ma...An essential step for the realization of free-form surface structures is to create an efficient structural gird that satisfies not only the architectural aesthetics,but also the structural performance.Employing the main stress trajectories as the representation of force flows on a free-form surface,an automatic grid generation approach is proposed for the architectural design.The algorithm automatically plots the main stress trajectories on a 3D free-form surface,and adopts a modified advancing front meshing technique to generate the structural grid.Based on the proposed algorithm,an automatic grid generator named "St-Surmesh" is developed for the practical architectural design of free-form surface structure.The surface geometry of one of the Sun Valleys in Expo Axis for the Expo Shanghai 2010 is selected as a numerical example for validating the proposed approach.Comparative studies are performed to demonstrate how different structural grids affect the design of a free-form surface structure.展开更多
With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu c...With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu ctive materials away and polishes work-piece of free-form surface. The study o f the contact force between the end of polishing tool and the surface of work-p iece is the key for the compliant EDM to study its cutting mechanism and to make better use of it. This paper makes a model for the contact force and verifies i t by experiments and simulation based on the theory of elastic body kinetics and dynamic stress concentration. The research work shows that this contact force i s caused by both the electrical impulsion of EDM and the mechanical force of ult rasonic vibration, the discharge frequency of compliant EDM has a much more clos er connection with the vibration frequency of polishing tool rather than the fre quency of ultrasonic vibration.展开更多
Carrying out experiments and researches on tool bre ak age and undercut of work-piece of free-form surface by using wavelet analysis, both the fault features can be extracted in a special frequency segment of wave let...Carrying out experiments and researches on tool bre ak age and undercut of work-piece of free-form surface by using wavelet analysis, both the fault features can be extracted in a special frequency segment of wave let decompose. According to the feature of transient fault, the author proposes for the first time the automatic determination technology of the threshold by us e of the adaptive filter characteristic of wavelet transform. Based on profound researches on steady fault feature, this dissertation makes an effective token o f steady fault feature by using wavelet energy method, and proposes the new idea to identify cut-in case and cut-out case, thereby successfully gives an uniqu e description quantitatively on the characterization of the variation of fault a nd cutting condition in the monitoring system.展开更多
地表颗粒物是城市雨水径流的主要污染源,也是多种径流污染物的主要载体,对其污染特征及规律的掌握是有效控制径流污染的关键。采用文献计量学方法,系统梳理2017—2023年国内外城市地表颗粒物研究报道,从物理化学特性、污染时空分布特征...地表颗粒物是城市雨水径流的主要污染源,也是多种径流污染物的主要载体,对其污染特征及规律的掌握是有效控制径流污染的关键。采用文献计量学方法,系统梳理2017—2023年国内外城市地表颗粒物研究报道,从物理化学特性、污染时空分布特征、污染源解析、累积过程与影响因素4个方面归纳总结城市地表颗粒物的研究进展。结果表明:Web of Science和中国知网数据库2017—2023年在城市地表颗粒物领域的发文量均呈现先上升后下降的趋势,中英文文献研究热点集中在重金属、多环芳烃(PAHs)、源解析、风险评价等方面;粒径是影响地表颗粒物携带污染物种类和含量的重要物理特性,地表颗粒物中新污染物如多环芳烃衍生物、微塑料等化学指标逐渐受到关注;城市商业区、交通区和工业区地表颗粒物中重金属、PAHs、微塑料等污染水平较高,而公园绿地中氮和磷含量较高;地表颗粒物污染显著的季节性差异与污染来源和气候因素有关;城市地表颗粒物中重金属来源于自然或人为活动,PAHs主要源于有机物不完全燃烧,氮和磷来源解析尚无定论;幂函数、指数函数、饱和函数等函数形式可较好地描述城市地表颗粒物累积过程。未来研究应重点关注污染物赋存形态及其迁移转化机制,深入探讨不同类型下垫面颗粒物时空演替规律及相应机制,精确解析不同类型污染物来源,并探索地表颗粒物累积过程普适性形式。展开更多
基金Project(51378457)supported by the National Natural Science Foundation of China
文摘An essential step for the realization of free-form surface structures is to create an efficient structural gird that satisfies not only the architectural aesthetics,but also the structural performance.Employing the main stress trajectories as the representation of force flows on a free-form surface,an automatic grid generation approach is proposed for the architectural design.The algorithm automatically plots the main stress trajectories on a 3D free-form surface,and adopts a modified advancing front meshing technique to generate the structural grid.Based on the proposed algorithm,an automatic grid generator named "St-Surmesh" is developed for the practical architectural design of free-form surface structure.The surface geometry of one of the Sun Valleys in Expo Axis for the Expo Shanghai 2010 is selected as a numerical example for validating the proposed approach.Comparative studies are performed to demonstrate how different structural grids affect the design of a free-form surface structure.
文摘With an elastic negative pole being driven by ultra so nic vibration and being moved along the surface of work-piece compliantly by ro bot, a new kind of effective EDM, the compliant EDM, cuts the electrically condu ctive materials away and polishes work-piece of free-form surface. The study o f the contact force between the end of polishing tool and the surface of work-p iece is the key for the compliant EDM to study its cutting mechanism and to make better use of it. This paper makes a model for the contact force and verifies i t by experiments and simulation based on the theory of elastic body kinetics and dynamic stress concentration. The research work shows that this contact force i s caused by both the electrical impulsion of EDM and the mechanical force of ult rasonic vibration, the discharge frequency of compliant EDM has a much more clos er connection with the vibration frequency of polishing tool rather than the fre quency of ultrasonic vibration.
文摘Carrying out experiments and researches on tool bre ak age and undercut of work-piece of free-form surface by using wavelet analysis, both the fault features can be extracted in a special frequency segment of wave let decompose. According to the feature of transient fault, the author proposes for the first time the automatic determination technology of the threshold by us e of the adaptive filter characteristic of wavelet transform. Based on profound researches on steady fault feature, this dissertation makes an effective token o f steady fault feature by using wavelet energy method, and proposes the new idea to identify cut-in case and cut-out case, thereby successfully gives an uniqu e description quantitatively on the characterization of the variation of fault a nd cutting condition in the monitoring system.
文摘地表颗粒物是城市雨水径流的主要污染源,也是多种径流污染物的主要载体,对其污染特征及规律的掌握是有效控制径流污染的关键。采用文献计量学方法,系统梳理2017—2023年国内外城市地表颗粒物研究报道,从物理化学特性、污染时空分布特征、污染源解析、累积过程与影响因素4个方面归纳总结城市地表颗粒物的研究进展。结果表明:Web of Science和中国知网数据库2017—2023年在城市地表颗粒物领域的发文量均呈现先上升后下降的趋势,中英文文献研究热点集中在重金属、多环芳烃(PAHs)、源解析、风险评价等方面;粒径是影响地表颗粒物携带污染物种类和含量的重要物理特性,地表颗粒物中新污染物如多环芳烃衍生物、微塑料等化学指标逐渐受到关注;城市商业区、交通区和工业区地表颗粒物中重金属、PAHs、微塑料等污染水平较高,而公园绿地中氮和磷含量较高;地表颗粒物污染显著的季节性差异与污染来源和气候因素有关;城市地表颗粒物中重金属来源于自然或人为活动,PAHs主要源于有机物不完全燃烧,氮和磷来源解析尚无定论;幂函数、指数函数、饱和函数等函数形式可较好地描述城市地表颗粒物累积过程。未来研究应重点关注污染物赋存形态及其迁移转化机制,深入探讨不同类型下垫面颗粒物时空演替规律及相应机制,精确解析不同类型污染物来源,并探索地表颗粒物累积过程普适性形式。
