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The Material Point Method (MPM) has been shown to facilitate effective simulations of physically complex and topologically challenging materials, with a wealth of emerging applications in computational engineering and visual computing. Borne out of the extreme importance of regularity, MPM is given attractive parallelization opportunities on high-performance modern multiprocessors. Parallelization of MPM that fully leverages computing resources presents challenges that require exploring an extensive design-space for favorable data structures and algorithms. Unlike the conceptually simple CPU parallelization, where the coarse partition of tasks can be easily applied, it takes greater effort to reach the GPU hardware saturation due to its many-core SIMT architecture. In this paper we introduce methods for addressing the computational challenges of MPM and extending the capabilities of general simulation systems based on MPM, particularly concentrating on GPU optimization. In addition to our open-source high-performance framework, we also conduct performance analyses and benchmark experiments to compare against alternative design choices which may superficially appear to be reasonable, but can suffer from suboptimal performance in practice. Our explicit and fully implicit GPU MPM solvers are further equipped with a Moving Least Squares MPM heat solver and a novel sand constitutive model to enable fast simulations of a wide range of materials. We demonstrate that more than an order of magnitude performance improvement can be achieved with our GPU solvers. Practical high-resolution examples with up to ten million particles run in less than one minute per frame.

Abstract Bioethanol is currently the only alternative to gasoline that can be used immediately without having to make any significant changes in the way fuel is distributed. In addition, the carbon dioxide (CO2) released during the combustion of bioethanol is the same as that used by the plant in the atmosphere for its growth, so it does not participate in the increase of the greenhouse effect. Bioethanol can be obtained by fermentation of plants containing sucrose (beet, sugar cane…) or starch (wheat, corn…). However, large-scale use of bioethanol implies the use of very large agricultural surfaces for maize or sugarcane production. Lignocellulosic biomass (LCB) such as agricultural residues for the production of bioethanol seems to be a solution to this problem due to its high availability and low cost even if its growth still faces technological difficulties. In this review, we present an overview of lignocellulosic biomass, the different methods of pre-treatment of LCB and the various fermentation processes that can be used to produce bioethanol from LCB.

In this paper, we present a mixed explicit and semi-implicit Material Point Method for simulating particle-laden flows. We develop a Multigrid Preconditioned fluid solver for the Locally Averaged Navier Stokes equation. This is discretized purely on a semi-staggered standard MPM grid. Sedimentation is modeled with the Drucker-Prager elastoplasticity flow rule, enhanced by a novel particle density estimation method for converting particles between representations of either continuum or discrete points. Fluid and sediment are two-way coupled through a momentum exchange force that can be easily resolved with two MPM background grids. We present various results to demonstrate the efficacy of our method.

Fig. 1. (Left)Water filling a river bed surrounded by a canyon, with effective resolution 512 2 × 1024. Three refinement levels are used, based on proximity to the terrain. (Right) Sources inject water into a container and collide to form a thin sheet, with effective resolution 512 3 . Adaptivity pattern shown on background.We present an efficient and scalable octree-inspired fluid simulation framework with the flexibility to leverage adaptivity in any part of the computational domain, even when resolution transitions reach the free surface. Our methodology ensures symmetry, definiteness and second order accuracy of the discrete Poisson operator, and eliminates numerical and visual artifacts of prior octree schemes. This is achieved by adapting the operators acting on the octree's simulation variables to reflect the structure and connectivity of a power diagram, which recovers primal-dual mesh orthogonality and eliminates problematic T-junction configurations. We show how such operators can be efficiently implemented using a pyramid of sparsely populated uniform grids, enhancing the regularity of operations and facilitating parallelization. A novel scheme is proposed for encoding the topology of the power diagram in the neighborhood of each octree cell, allowing us to locally reconstruct it on the fly via a lookup table, rather than resorting to costly explicit meshing. The pressure Poisson equation is solved via a highly efficient, matrix-free multigrid preconditioner for Conjugate Gradient, adapted to the power diagram discretization. We use another sparsely † M. Aanjaneya and M. Gao are joint first authors. * M. Aanjaneya was with the University of Wisconsin -Madison during this work. This work was supported in part by National Science Foundation grants IIS-1253598, CCF-1423064, CCF-1533885 and by the Natural Sciences and Engineering Research Council of Canada under grant RGPIN-04360-2014. The authors are grateful to Nathan Mitchell for his indispensable help with modeling and rendering of examples. C. Batty would like to thank Ted Ying for carrying out preliminary explorations on quadtrees. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from permissions@acm.org. populated uniform grid for high resolution interface tracking with a narrow band level set representation. Using the recently introduced SPGrid data structure, sparse uniform grids in both the power diagram discretization and our narrow band level set can be compactly stored and efficiently updated via streaming operations. Additionally, we present enhancem...