The Micro- and Nano-mechanics Working Group of the Chinese Society of Theoretical and Applied Mechanics organized a forum to discuss the perspectives, trends, and directions in mechanics of heterogeneous materials in ...The Micro- and Nano-mechanics Working Group of the Chinese Society of Theoretical and Applied Mechanics organized a forum to discuss the perspectives, trends, and directions in mechanics of heterogeneous materials in January 2010. The international journal, Acta Mechanica Solida Sinica, is de- voted to all fields of solid mechanics and relevant disciplines in science, technology, and engineering, with a balanced coverage on analytical, experimental, numerical and applied investigations. On the occasion of the 30TM anniversary of Acta Mechanica Solida Sinica, its editor-in-chief, Professor Q.S. Zheng invited some of the forum participants to review the state-of-the-art of mechanics of heterogeneous solids, with a particular emphasis on the recent research development results of Chinese scientists. Their reviews are organized into five research areas as reported in different sections of this paper. ~I firstly brings in fo- cus on micro- and nano-mechanics, with regards to several selective topics, including multiscale coupled models and computational methods, nanocrystal superlattices, surface effects, micromechanical damage mechanics, and microstructural evolution of metals and shape memory alloys. ~II shows discussions on multifield coupled mechanical phenomena, e.g., multi-fields actuations of liquid crystal polymer networks, mechanical behavior of materials under radiations, and micromechanics of heterogeneous materials. In ~III, we mainly address the multiscale mechanics of biological nanocomposites, biological adhesive surface mechanics, wetting and dewetting phenomena on microstructured solid surfaces. The phononic crystals and manipulation of elastic waves were elaborated in ~IV. Finally, we conclude with a series of perspectives on solid mechanics. This review will set a primary goal of future science research and engineering application on solid mechanics with the effort of social and economic development.展开更多
Terrestrial evapotranspiration(ET)is a crucial link between Earth’s water cycle and the surface energy budget.Accurate measurement and estimation remain a major challenge in geophysical,biological,and environmental s...Terrestrial evapotranspiration(ET)is a crucial link between Earth’s water cycle and the surface energy budget.Accurate measurement and estimation remain a major challenge in geophysical,biological,and environmental studies.Pioneering work,represented by Dalton and Penman,and the development of theories and experiments on turbulent exchange in the atmospheric boundary layer(ABL),laid the foundation for mainstream methodologies in ET estimation.Since the 1990s,eddy covariance(EC)systems and satellite remote sensing have been widely applied from cold to tropical and from arid to humid regions.They cover water surfaces,wetlands,forests,croplands,grasslands,barelands,and urban areas,offering an exceptional number of reports on diverse ET processes.Surface nocturnal ET,hysteresis between ET and environmental forces,turbulence intermittency,island effects on heterogeneous surfaces,and phase transition between underlying surfaces are examples of reported new phenomena,posing theoretical and practical challenges to mainstream ET methodologies.Additionally,based on non-conventional theories,new methods have emerged,such as maximum entropy production and nonparametric approaches.Furthermore,high-frequency on-site observation and aerospace remote sensing technology in combination form multi-scale observations across plant stomata,leaves,plants,canopies,landscapes,and basins.This promotes an insightful understanding of diverse ET processes and synthesizes the common mechanisms of the processes between and across spatial and temporal scales.All the recent achievements in conception,model,and technology serve as the basis for breaking through the known difficulties in ET estimation.We expect that they will provide a rigorous,reliable scientific basis and experimental support to address theoretical arguments of global significance,such as the water-heat-carbon cycle,and solve practical needs of national importance,including agricultural irrigation and food security,precise management of water resources and eco-environmental pr展开更多
The accurate determination of surface-layer turbulent fluxes over urban areas is critical to understanding urban boundary layer （UBL） evolution. In this study, a remote-sensing technique using a large aperture scint...The accurate determination of surface-layer turbulent fluxes over urban areas is critical to understanding urban boundary layer （UBL） evolution. In this study, a remote-sensing technique using a large aperture scintillometer （LAS） was investigated to estimate surface-layer turbulent fluxes over a highly heterogeneous urban area. The LAS system, with an optical path length of 2.1 km, was deployed in an urban area characterized by a complicated land-use mix （residential houses, water body, bare ground, etc.）. The turbulent sensible heat （QH） and momentum fluxes （z） were estimated from the scintillation measurements obtained from the LAS system during the cold season. Three-dimensional LAS footprint modeling was introduced to identify the source areas （＂footprint＂） of the estimated turbulent fluxes. The analysis results showed that the LAS-derived turbulent fluxes for the highly heterogeneous urban area revealed reasonable temporal variation during daytime on clear days, in comparison to the land-surface process-resolving numerical modeling. A series of sensitivity tests indicated that the overall uncertainty in the LAS-derived daytime QH was within 20%-30% in terms of the influence of input parameters and the non- dimensional similarity function for the temperature structure function parameter, while the estimation errors in z were less sensitive to the factors of influence, except aerodynamic roughness length. The 3D LAS footprint modeling characterized the source areas of the LAS-derived turbulent fluxes in the heterogeneous urban area, revealing that the representative spatial scales of the LAS system deployed with the 2.1 km optical path distance ranged from 0.2 to 2 km2 （a ＂micro-a scale＂）, depending on local meteorological conditions.展开更多
The conventional isosurface techniques are not competent for nleshing a heterogeneous object because they assume that the object is homogeneous. Thus the visualization method taking the heterogeneity into account is d...The conventional isosurface techniques are not competent for nleshing a heterogeneous object because they assume that the object is homogeneous. Thus the visualization method taking the heterogeneity into account is desired. In this paper, we propose a novel algorithm to extract the boundary surfaces from a heterogeneous object in one pass, whose remarkable advantage is free of the number of materials contained. The heterogeneous object is first classified into a series of homogeneous material components. Then each component is enclosed with a 2D-manifold boundary surface extracted via our algorithm. The information important to the heterogeneous object is also provided, such as the interface between two materials, the intersection curve where three materials meet and the intersection point where four materials meet. To improve the performance, the algorithm is also designed and implemented on GPU. Experimental results demonstrate the effectiveness and efficiency of the proposed algorithm.展开更多
文摘The Micro- and Nano-mechanics Working Group of the Chinese Society of Theoretical and Applied Mechanics organized a forum to discuss the perspectives, trends, and directions in mechanics of heterogeneous materials in January 2010. The international journal, Acta Mechanica Solida Sinica, is de- voted to all fields of solid mechanics and relevant disciplines in science, technology, and engineering, with a balanced coverage on analytical, experimental, numerical and applied investigations. On the occasion of the 30TM anniversary of Acta Mechanica Solida Sinica, its editor-in-chief, Professor Q.S. Zheng invited some of the forum participants to review the state-of-the-art of mechanics of heterogeneous solids, with a particular emphasis on the recent research development results of Chinese scientists. Their reviews are organized into five research areas as reported in different sections of this paper. ~I firstly brings in fo- cus on micro- and nano-mechanics, with regards to several selective topics, including multiscale coupled models and computational methods, nanocrystal superlattices, surface effects, micromechanical damage mechanics, and microstructural evolution of metals and shape memory alloys. ~II shows discussions on multifield coupled mechanical phenomena, e.g., multi-fields actuations of liquid crystal polymer networks, mechanical behavior of materials under radiations, and micromechanics of heterogeneous materials. In ~III, we mainly address the multiscale mechanics of biological nanocomposites, biological adhesive surface mechanics, wetting and dewetting phenomena on microstructured solid surfaces. The phononic crystals and manipulation of elastic waves were elaborated in ~IV. Finally, we conclude with a series of perspectives on solid mechanics. This review will set a primary goal of future science research and engineering application on solid mechanics with the effort of social and economic development.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51879255,41430855).
文摘Terrestrial evapotranspiration(ET)is a crucial link between Earth’s water cycle and the surface energy budget.Accurate measurement and estimation remain a major challenge in geophysical,biological,and environmental studies.Pioneering work,represented by Dalton and Penman,and the development of theories and experiments on turbulent exchange in the atmospheric boundary layer(ABL),laid the foundation for mainstream methodologies in ET estimation.Since the 1990s,eddy covariance(EC)systems and satellite remote sensing have been widely applied from cold to tropical and from arid to humid regions.They cover water surfaces,wetlands,forests,croplands,grasslands,barelands,and urban areas,offering an exceptional number of reports on diverse ET processes.Surface nocturnal ET,hysteresis between ET and environmental forces,turbulence intermittency,island effects on heterogeneous surfaces,and phase transition between underlying surfaces are examples of reported new phenomena,posing theoretical and practical challenges to mainstream ET methodologies.Additionally,based on non-conventional theories,new methods have emerged,such as maximum entropy production and nonparametric approaches.Furthermore,high-frequency on-site observation and aerospace remote sensing technology in combination form multi-scale observations across plant stomata,leaves,plants,canopies,landscapes,and basins.This promotes an insightful understanding of diverse ET processes and synthesizes the common mechanisms of the processes between and across spatial and temporal scales.All the recent achievements in conception,model,and technology serve as the basis for breaking through the known difficulties in ET estimation.We expect that they will provide a rigorous,reliable scientific basis and experimental support to address theoretical arguments of global significance,such as the water-heat-carbon cycle,and solve practical needs of national importance,including agricultural irrigation and food security,precise management of water resources and eco-environmental pr
基金supported by the Korea Meteorological Administration Research and Development Program (Grant No. CATER 2012-3081)
文摘The accurate determination of surface-layer turbulent fluxes over urban areas is critical to understanding urban boundary layer （UBL） evolution. In this study, a remote-sensing technique using a large aperture scintillometer （LAS） was investigated to estimate surface-layer turbulent fluxes over a highly heterogeneous urban area. The LAS system, with an optical path length of 2.1 km, was deployed in an urban area characterized by a complicated land-use mix （residential houses, water body, bare ground, etc.）. The turbulent sensible heat （QH） and momentum fluxes （z） were estimated from the scintillation measurements obtained from the LAS system during the cold season. Three-dimensional LAS footprint modeling was introduced to identify the source areas （＂footprint＂） of the estimated turbulent fluxes. The analysis results showed that the LAS-derived turbulent fluxes for the highly heterogeneous urban area revealed reasonable temporal variation during daytime on clear days, in comparison to the land-surface process-resolving numerical modeling. A series of sensitivity tests indicated that the overall uncertainty in the LAS-derived daytime QH was within 20%-30% in terms of the influence of input parameters and the non- dimensional similarity function for the temperature structure function parameter, while the estimation errors in z were less sensitive to the factors of influence, except aerodynamic roughness length. The 3D LAS footprint modeling characterized the source areas of the LAS-derived turbulent fluxes in the heterogeneous urban area, revealing that the representative spatial scales of the LAS system deployed with the 2.1 km optical path distance ranged from 0.2 to 2 km2 （a ＂micro-a scale＂）, depending on local meteorological conditions.
基金supported by the National Natural Science Foundation of China under Grant Nos. 60933007 and 61170138the National Basic Research 973 Program of China under Grant No. 2009CB320801the Program for New Century Excellent Talents in University of Ministry of Education of China under Grant No. NCET-10-0728
文摘The conventional isosurface techniques are not competent for nleshing a heterogeneous object because they assume that the object is homogeneous. Thus the visualization method taking the heterogeneity into account is desired. In this paper, we propose a novel algorithm to extract the boundary surfaces from a heterogeneous object in one pass, whose remarkable advantage is free of the number of materials contained. The heterogeneous object is first classified into a series of homogeneous material components. Then each component is enclosed with a 2D-manifold boundary surface extracted via our algorithm. The information important to the heterogeneous object is also provided, such as the interface between two materials, the intersection curve where three materials meet and the intersection point where four materials meet. To improve the performance, the algorithm is also designed and implemented on GPU. Experimental results demonstrate the effectiveness and efficiency of the proposed algorithm.
