Unstructured mesh partition improvement for implicit finite element at extreme scale

Parallel simulations at extreme scale require that the mesh is distributed across a large number of processors with equal work load and minimum inter-part communications. A number of algorithms have been developed to meet these goals and graph/hypergraph-based methods are by far the most powerful ones. However, the global implementation of current approaches can fail on very large core counts and the vertex imbalance is not optimal where individual cores are lightly loaded. Those issues are resolved by combination of global and local partitioning and an iterative improvement algorithm, LIIPBMod, developed in the previous study (Zhou et al. in SIAM J. Sci. Comput. 32:3201–3227, 2010). In the current work, this combined partition strategy is applied to the simulations at extreme scale with up to O(10¹⁰) elements and up to O(300K) cores. Strong scaling studies on IBM BlueGene/P and Cray XT5 systems demonstrate the effectiveness of this combined partition algorithm.     

Study of Electromagnetic Properties of Fabricated NiFe2O4/Polyurethane Nanocomposites

Nickel ferrite loaded (NiFe₂O₄) segmented polyurethane (SPU) nanocomposites prepared by melt mixing method using microcompounder at temperature 185 °C in recirculation mode to ensure proper dispersion and distribution of nanoparticles at optimized residency time of 5 min. Three different weight percentages of nanocomposites (3, 5, and 10 wt %) was prepared and studied the electromagnetic property of nanocomposites obtained from complex permittivity and permeability. The effect of nanofiller (NiFe₂O₄) has been studied to assess their thermal properties using thermogravimetric analysis, differential scanning calorimetry, and thermomechanical analysis. The nanocomposites (NiFe₂O₄/SPU) have further been studied using FE-SEM, and the micrographs show embedded NiFe₂O₄ filler uniformly dispersed in SPU matrix without agglomeration (size 20–40 nm). It is also evident that further loading of nanofiller resulted in saturation effect yielding no applicable change in thermal behavior and revealed lesser melting enthalpy due to the coalescence of the nanofillers. X-ray diffraction and vibrating sample magnetometer also support the formation of the nanocomposite. The electric and magnetic properties of NiFe₂O₄ incorporated nanocomposite (NiFe₂O₄/SPU) may have potential application in microwave absorption. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48645.     

Clustering on a hypercube multicomputer

Squared error clustering algorithms for single-instruction multiple-data (SIMD) hypercubes are presented. The algorithms are shown to be asymptotically faster than previously known algorithms and require less memory per processing element (PE). For a clustering problem with N patterns, M features per pattern, and K clusters, the algorithms complete in O(k+log NM ) steps on NM processor hypercubes. This is optimal up to a constant factor. These results are extended to the case in which NMK processors are available. Experimental results from a multiple-instruction, multiple-data (MIMD) medium-grain hypercube are also presented     

Understanding granular mixing to enhance coating performance in a pan coater: Experiments and simulations

The knowledge of the particle flow and mixing in a pan coater is critical to optimize the design and operation of coating equipment. Mixing is an important but poorly understood aspect of coating of pharmaceutical dosage forms (tablets). Our study focuses on the fundamental mechanisms of granular flow and mixing and their relationship to the coating performance. A quantitative method is developed and validated to characterize the mixing process throughout the mixing vessel. This method is used to establish a baseline determination of mixing homogeneity as a function of various mixing conditions. White and red non-pareils of 5–6 mesh size are loaded in the ellipsoid pan coater to check the effect of initial loading (side–side and front–back), fill level, orientation of the vessel and the vessel speed on granular mixing. Video-imaging and discrete-pocket samplers are used to quantify mixing and to finally estimate the optimal operating conditions. DEM (Discrete Element Method) based numerical model was also developed to study the effect of granular mixing in a pan coater. When the axis of rotation of the mixer is horizontal (no tilt), slower axial dispersion is observed in both the experiments and simulations, than the radial convection. However, tilt enhances axial mixing, and faster axial mixing is seen for higher tilt angles from the horizontal. The speed of the rotating vessel has a nominal effect on the rate of mixing in a coating pan, as observed from the experimental and simulation studies. Moreover, fill level has no significant effect on the rate of mixing. Coating experiments are performed in the pan coater where white non-pareils being coated by spraying Opadry II solution. DEM simulation of coating is performed with post processing particle dynamics data. The effects of various operational and spray parameters are determined on the coating performance. Optimal coating performance is attained at an optimal mixing condition.     

Quantifying drying performance of a filter dryer: Experiments and simulations

Drying is one of the most commonly used unit operations in the preparation of dry granules by thermally removing volatile solvent from the wet solid. The study focuses on the quantitative investigation of heat transfer in a filter dryer in the quest to determine the optimum drying conditions. Consequently, contact drying kinetics of glassbeads–ethanol and lactose–ethanol system is investigated using an agitated filter dryer (Charles Thompson). Discrete element method is employed to simulate granular flow, mixing and heat transport in the vessel. Typical system with glass beads is numerically simulated using appropriate material properties and validated by the experimental findings. A parametric study for both simulations and experiments is performed to assess the effect of various conditions of wall temperature, fill level and impeller speed on the drying performance in the filter dryer. A high wall temperature showed an increase in the drying rate and a sharp rise in the average bed temperature, thereby decreasing the total time for drying operation. An increase in fill volume (bed depth) at constant wall temperature and speed resulted in a decline in the drying rate. The rotational speed had a nominal impact on drying of glass beads. Hence low rotational speeds seemed optimal for contact drying.     

Titanium Foams Processed Through Powder Metallurgy Route Using Lubricant Acrawax as Space Holder Material

In the present work titanium foams have been synthesized using acrawax as the space holder material. Acrawax has generally been used as a lubricant for easier compaction of aluminium alloy powders. This study deals with the use of this space holder material in the form of beads for creating pores in titanium metal matrix. Acrawax facilitates the formation of continuous dense cell walls which is difficult to obtain using ordinary space holder materials. Moreover, acrawax is compressible in nature and it facilitates the formation of better and uniformly sized pores. Titanium foams have been synthesized utilizing acrawax in two different sizes. The effect of using differently sized acrawax on the cell walls and mechanical properties has also been carried out in this study.     

Which separation scenarios are advantageous for membranes or distillations?

We systematically analyze power requirements of membrane and distillation processes for binary mixtures where the desired product component is more permeable and also more volatile. We first derive a shortcut method to compare the efficiency of heat pump and steam-driven distillations. Then, power requirements of heat pump distillation and membrane separation are discussed. Distillation generally requires lower power when either high component recoveries are needed (at all tested product purities), or high purity product streams with modest recoveries are needed. For high purity products at modest recoveries, membranes have a potential to provide energy benefits for highly enriched feeds, especially those composed of close boiling components. Additionally, when feed concentration is moderate to high and product recovery and purity are modest, membranes are likely to show efficiency gain. For the advantageous distillation scenarios studied, the power was generally lower than the membranes by a factor of two to seven.