Browsing by Author "Tang, J"

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    Dense granular flow - A collaborative study
    (Powder Technology, 2015-11-01) Mort, P; Michaels, JN; Behringer, RP; Campbell, CS; Kondic, L; Kheiripour Langroudi, M; Shattuck, M; Tang, J; Tardos, GI; Wassgren, C
    © 2015 Elsevier B.V..The International Fine Powder Research Institute (IFPRI) has funded an extensive program in dry powder and granular flows, including a focused study on dense flows of interest to a range of industrial handling and process unit operations, especially dense flows at relatively high shear rates. The dense flow program included experimental studies of granular rheology in 3D axial Couette and 2D hopper geometries, wherein the effect of force chains and jamming interactions were investigated as relevant to flow, stress and packing dynamics. The program cumulated in a collaborative study funded by the NSF, wherein a group of academic collaborators was invited to model experimental systems used in IFPRI-sponsored projects. This paper provides a summary of the IFPRI program, details of the collaborative modeling study, and perspective on what is needed to progress the work further.
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    Large trees drive forest aboveground biomass variation in moist lowland forests across the tropics
    (Global Ecology and Biogeography, 2013-12) Slik, JWF; Paoli, G; Mcguire, K; Amaral, I; Barroso, J; Bastian, M; Blanc, L; Bongers, F; Boundja, P; Clark, C; Collins, M; Dauby, G; Ding, Y; Doucet, J-L; Eler, E; Ferreira, L; Forshed, O; Fredriksson, G; Gillet, J-F; Harris, D; Leal, M; Laumonier, Y; Malhi, Y; Mansor, A; Martin, E; Miyamoto, K; Araujo-Murakami, A; Nagamasu, H; Nilus, R; Nurtjahya, E; Oliveira, A; Onrizal, O; Parada-Gutierrez, A; Permana, A; Poorter, L; Poulsen, J; Ramirez-Angulo, H; Reitsma, J; Rovero, F; Rozak, A; Sheil, D; Silva-Espejo, J; Silveira, M; Spironelo, W; ter Steege, H; Stevart, T; Navarro-Aguilar, GE; Sunderland, T; Suzuki, E; Tang, J; Theilade, I; van der Heijden, G; van Valkenburg, J; Van Do, T; Vilanova, E; Vos, V; Wich, S; Wöll, H; Yoneda, T; Zang, R; Zhang, M-G; Zweifel, N
    Aim: Large trees (d.b.h.≥70cm) store large amounts of biomass. Several studies suggest that large trees may be vulnerable to changing climate, potentially leading to declining forest biomass storage. Here we determine the importance of large trees for tropical forest biomass storage and explore which intrinsic (species trait) and extrinsic (environment) variables are associated with the density of large trees and forest biomass at continental and pan-tropical scales. Location: Pan-tropical. Methods: Aboveground biomass (AGB) was calculated for 120 intact lowland moist forest locations. Linear regression was used to calculate variation in AGB explained by the density of large trees. Akaike information criterion weights (AICc-wi) were used to calculate averaged correlation coefficients for all possible multiple regression models between AGB/density of large trees and environmental and species trait variables correcting for spatial autocorrelation. Results: Density of large trees explained c. 70% of the variation in pan-tropical AGB and was also responsible for significantly lower AGB in Neotropical [287.8 (mean)±105.0 (SD) Mg ha-1] versus Palaeotropical forests (Africa 418.3±91.8 Mg ha-1; Asia 393.3±109.3 Mg ha-1). Pan-tropical variation in density of large trees and AGB was associated with soil coarseness (negative), soil fertility (positive), community wood density (positive) and dominance of wind dispersed species (positive), temperature in the coldest month (negative), temperature in the warmest month (negative) and rainfall in the wettest month (positive), but results were not always consistent among continents. Main conclusions: Density of large trees and AGB were significantly associated with climatic variables, indicating that climate change will affect tropical forest biomass storage. Species trait composition will interact with these future biomass changes as they are also affected by a warmer climate. Given the importance of large trees for variation in AGB across the tropics, and their sensitivity to climate change, we emphasize the need for in-depth analyses of the community dynamics of large trees. © 2013 John Wiley & Sons Ltd.
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    Orientation, flow, and clogging in a two-dimensional hopper: Ellipses vs. disks
    (EPL, 2016-05-01) Tang, J; Behringer, RP
    © EPLA, 2016.Two-dimensional (2D) hopper flow of disks has been extensively studied. Here, we investigate hopper flow of ellipses with aspect ratio α = 2, and we contrast that behavior to the flow of disks. We use a quasi-2D hopper containing photoelastic particles to obtain stress/force information. We simultaneously measure the particle motion and stress. We determine several properties, including discharge rates, clogging probabilities, and the number of particles in clogging arches. For both particle types, the size of the opening, D, relative to the size of particles, ℓ, is an important dimensionless measure. The orientation of the ellipses plays an important role in flow rheology and clogging. The alignment of contacting ellipses enhances the probability of forming stable arches. This study offers insights into applications involving the flow of granular materials consisting of ellipsoidal shapes, and possibly other non-spherical shapes.