77 research outputs found
A Globally Conforming Lattice Structure for 2D Stress Tensor Visualization
No full textWe present a visualization technique for 2D stress tensor fields based on the construction of a globally conforming lattice. Conformity ensures that the lattice edges follow the principal stress directions and the aspect ratio of lattice elements represents the stress anisotropy. Since such a lattice structure cannot be space-filling in general, it is constructed from multiple intersecting lattice beams. Conformity at beam intersections is ensured via a constrained optimization problem, by computing the aspect ratio of elements at intersections so that their edges meet when continued along the principal stress lines. In combination with a coloring scheme that encodes relative stress magnitudes, a global visualization is achieved. By introducing additional constraints on the positional variation of the beam intersections, coherent visualizations are achieved when external loads or material parameters are changed. In a number of experiments using non-trivial scenarios, we demonstrate the capability of the proposed visualization technique to show the global and local structure of a given stress field.Accepted Author ManuscriptMaterials and Manufacturin
Stress topology analysis for porous infill optimization
No full textThe optimization of porous infill structures via local volume constraints has become a popular approach in topology optimization. In some design settings, however, the iterative optimization process converges only slowly, or not at all even after several hundreds or thousands of iterations. This leads to regions in which a distinct binary design is difficult to achieve. Interpreting intermediate density values by applying a threshold results in large solid or void regions, leading to sub-optimal structures. We find that this convergence issue relates to the topology of the stress tensor field that is simulated when applying the same external forces on the solid design domain. In particular, low convergence is observed in regions around so-called trisector degenerate points. Based on this observation, we propose an automatic initialization process that prescribes the topological skeleton of the stress field into the density field as solid simulation elements. These elements guide the material deposition around the degenerate points, but can also be remodelled or removed during the optimization. We demonstrate significantly improved convergence rates in a number of use cases with complex stress topologies. The improved convergence is demonstrated for infill optimization under homogeneous as well as spatially varying local volume constraints.Materials and Manufacturin
Spatial and Temporal Variation of Wind Erosion Climatic Erosivity and Its Response to ENSO in the Otindag Desert, China
No full textWind erosion is a major cause of soil losses in China’s drylands which is further stimulated by climate variability and fragile ecological conditions. Climatic erosivity is an important index of wind erosion, therefore, evaluation of its spatiotemporal variations and relationship with the El Niño–Southern Oscillation (ENSO) will provide a theoretical basis for the comprehensive management and prevention of soil erosion. In this study, by using the climatic erosivity equation, geographic information system (GIS) and geostatistical analysis, we quantified the climatic erosivity, explored its spatiotemporal variations, and detected the effects of the Multivariate ENSO Index (MEI) on climatic erosivity in the Otindag Desert during the period of 1980–2016. The results indicated that the climatic erosivity (C-factor value) ranged from 82–445, and it decreased from the western margin to the eastern margin of the desert. The climatic erosivity showed a significant downward trend at seasonal and annual scales (p < 0.05). As far as spring, autumn and annual climatic erosivity, the whole region showed a downward trend, however, the summer and winter climatic erosivity varied spatially, in which the central and western regions showed a downward trend, but the eastern region showed an upward trend. The results showed that the average climatic erosivity is weaker during La Niña events than during El Niño events. The climatic erosivity recorded by 14 of the 20 meteorological stations, all located in central and west regions, exhibited a significant correlation with MEI (p < 0.05). The ENSO has a significant impact on climatic erosivity
Design and development of commercial construction robotic system for waterproofing & insulation composite panel construction scenarios
No full textConstruction robots have been researched and explored or commercially tried in numerous construction processes such as facade painting, but few have achieved widespread commercial application. Waterproofing and insulation composite panel construction, related to building structural safety and energy consumption, is also plagued by rising labor costs, uncontrollable construction quality, and low efficiency, while research into construction robotics related to this issue is minimal. Thus, this paper explores and investigates the feasibility of developing a commercial robotic construction system for the waterproofing and insulation composite panel construction scenario. By analyzing the factors influencing construction robot procurement, existing construction processes, stakeholders, market demand, and feedback from interviews with contractor companies, the author developed two generations of prototypes for construction site testing. The test results and market feedback of the commercial grade prototypes confirm the feasibility of the commercial robotic construction system for waterproofing and insulation composite panel construction scenarios and provide a research case study of a commercial construction robot in the examined field that includes both theoretical analysis and commercial purchasing decision reference.</p
A Streamline-guided De-Homogenization Approach for Structural Design
No full textWe present a novel de-homogenization approach for efficient design of
high-resolution load-bearing structures. The proposed approach builds upon a
streamline-based parametrization of the design domain, using a set of
space-filling and evenly-spaced streamlines in the two mutually orthogonal
direction fields that are obtained from homogenization-based topology
optimization. Streamlines in these fields are converted into a graph, which is
then used to construct a quad-dominant mesh whose edges follow the direction
fields. In addition, the edge width is adjusted according to the density and
anisotropy of the optimized orthotropic cells. In a number of numerical
examples, we demonstrate the mechanical performance and regular appearance of
the resulting structural designs, and compare them with those from classic and
contemporary approaches.Comment: 10 pages, 13 figures, submitted to Journal, under revie
Global warming reduces plant reproductive output for temperate multi-inflorescence species on the Tibetan plateau
No full textTemperature is projected to increase more during the winter than during the summer in cold regions. The effects of winter warming on reproductive effort have not been examined for temperate plant species. Here, we report the results of experimentally induced seasonal winter warming (0.4 and 2.4 degrees C increases in growing and nongrowing seasons, respectively, using warmed and ambient open-top chambers in a Tibetan Plateau alpine meadow) for nine indeterminate-growing species producing multiple (single-flowered or multi-flowered) inflorescences and three determinate-growing species producing single inflorescences after a 3-yr period of warming. Warming reduced significantly flower number and seed production per plant for all nine multi-inflorescence species, but not for the three single-inflorescence species. Warming had an insignificant effect on the fruit to flower number ratio, seed size and seed number per fruit among species. The reduction in seed production was largely attributable to the decline in flower number per plant. The flowering onset time was unaffected for nine of the 12 species. Therefore, the decline in flower production and seed production in response to winter warming probably reflects a physiological response (e.g. metabolic changes associated with flower production). Collectively, the data indicate that global warming may reduce flower and seed production for temperate herbaceous species and will probably have a differential effect on single- vs multi-inflorescence species
3D-TSV: The 3D Trajectory-based Stress Visualizer
No full textWe present the 3D Trajectory-based Stress Visualizer (3D-TSV), a visual
analysis tool for the exploration of the principal stress directions in 3D
solids under load. 3D-TSV provides a modular and generic implementation of key
algorithms required for a trajectory-based visual analysis of principal stress
directions, including the automatic seeding of space-filling stress lines,
their extraction using numerical schemes, their mapping to an effective
renderable representation, and rendering options to convey structures with
special mechanical properties. In the design of 3D-TSV, several perceptual
challenges have been addressed when simultaneously visualizing three mutually
orthogonal stress directions via lines. We present a novel algorithm for
generating a space-filling and evenly spaced set of mutually orthogonal lines.
The algorithm further considers the locations of lines to obtain a more regular
appearance, and enables the extraction of a level-of-detail representation with
adjustable sparseness of the trajectories along a certain stress direction. To
convey ambiguities in the orientation of the principal stress directions, the
user can select a combined visualization of two principal directions via
oriented ribbons. Additional depth cues improve the perception of the spatial
relationships between trajectories. 3D-TSV is accessible to end users via a
C++- and OpenGL-based rendering frontend that is seamlessly connected to a
MatLab-based extraction backend. The code (BSD license) of 3D-TSV as well as
scripts to make ANSYS and ABAQUS simulation results accessible to the 3D-TSV
backend are publicly available.Comment: 13 page
Responses of Bacterial Communities to Simulated Climate Changes in Alpine Meadow Soil of the Qinghai-Tibet Plateau
No full textThe soil microbial community plays an important role in terrestrial carbon and nitrogen cycling. However, microbial responses to climate warming or cooling remain poorly understood, limiting our ability to predict the consequences of future climate changes. To address this issue, it is critical to identify microbes sensitive to climate change and key driving factors shifting microbial communities. In this study, alpine soil transplant experiments were conducted downward or upward along an elevation gradient between 3,200 and 3,800 min the Qinghai-Tibet plateau to simulate climate warming or cooling. After a 2-year soil transplant experiment, soil bacterial communities were analyzed by pyrosequencing of 16S rRNA gene amplicons. The results showed that the transplanted soil bacterial communities became more similar to those in their destination sites and more different from those in their "home" sites. Warming led to increases in the relative abundances in Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria and decreases in Acidobacteria, Betaproteobacteria, and Deltaproteobacteria, while cooling had opposite effects on bacterial communities (symmetric response). Soil temperature and plant biomass contributed significantly to shaping the bacterial community structure. Overall, climate warming or cooling shifted the soil bacterial community structure mainly through species sorting, and such a shift might correlate to important biogeochemical processes such as greenhouse gas emissions. This study provides new insights into our understanding of soil bacterial community responses to climate warming and cooling
The Recycling of Ferric Salt in Steel Pickling Liquors: Preparation of Nano-sized Iron Oxide
No full textAbstractA novel process of recycling ferric salt in Steel Spent Pickling Liquors (SPL) is reported in this paper which refers to the combination of vacuum evaporation and preparation of nano-sized iron oxide (α-Fe2O3) by precipitation method. This study investigates the effect of ammonia concentration, Fe2+ concentration, reaction temperature, stirring speed and calcine temperature on the preparation of α-Fe2O3 by single factor experiment and the optimal preparation conditions of preparing α-Fe2O3 by orthogonal experiment. The results show that the concentration of Fe2O3 in product is up to 98.87%, and the average crystal diameter is about 31.3nm under optimized technological conditions, which realized the highest recycling rate of Fe at 85.6%
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