Person: Rycroft, Christopher
Loading...
Email Address
AA Acceptance Date
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
Rycroft
First Name
Christopher
Name
Rycroft, Christopher
7 results
Search Results
Now showing 1 - 7 of 7
Publication Modelling Intergranular and Transgranular Micro-Cracking in Polycrystalline Materials(Elsevier BV, 2018-02) Gulizzi, V; Rycroft, Christopher; Benedetti, IIn this work, a grain boundary formulation for intergranular and transgranular micro-cracking in three-dimensional polycrystalline aggregates is presented. The formulation is based on the displacement and stress boundary integral equations of solid mechanics and it has the advantage of expressing the polycrystalline problem in terms of grain boundary variables only. The individual grains within the polycrystalline morphology are modelled as generally anisotropic linear elastic domains with random spatial orientation. Transgranular micro-cracking is assumed to occur along specific cleavage planes, whose orientation in space within the grains depend upon the crystallographic lattice. Both intergranular and transgranular micro-cracking are modelled using suitably defined cohesive laws, whose parameters characterise the behaviour of the two mechanisms. The algorithm developed to track the inter/transgranular micro-cracking history is presented and discussed. Several numerical tests involving pseudo-3D and fully 3D morphologies are performed and analysed. The presented numerical results show that the developed formulation is capable of tracking the initiation and evolution of both intergranular and transgranular cracking as well as their competition, thus providing a useful tool for the study of damage micro-mechanics.Publication MeshVoro: A three-dimensional Voronoi mesh building tool for the TOUGH family of codes(Elsevier BV, 2014) Freeman, C.M.; Boyle, K.L; Reagan, M.; Johnson, J; Rycroft, Christopher; Moridis, G.J.Few tools exist for creating and visualizing complex three-dimensional simulation meshes,and these have limitations that restrict their application to particular geometries and circumstances. Mesh generation needs to trend toward evermore general applications. To that end,we have developed Mesh Voro, a tool that is based on the Voroþþ (Chris H. Rycroft,2009. Chaos19,041111)library and is capable of generating complex three dimensional Voro noitessellation-based(unstructured)meshes for the solution of problems of flow and transport in subsurface geologic media that are addressed by the TOUGH (Pruess,K.,Oldenbur gC.,Moridis G.,1999.ReportLBNL43134,582.Lawrence Berkeley National Laboratory,Berkeley,CA)family of codes. MeshVoro,which includes built-in data visualization routines, is a particularly useful tool because it extends the applicability of the TOUGH family of codes by enabling the scientifically robust and relatively easy discretization of systems with challenging3Dgeometries. We describe several applications of MeshVoro. We illustrate the ability of the tool to straight forwardly transform a complex geological grid in to a simulation mesh that conforms to the specifications of the TOUGH family of codes. We demonstrate how MeshVoro can describe complex system geometries with a relatively small number of gridblocks, and we construct meshes for geometries that would have been practically intractable with a standard Cartesian gridapproach. We also discuss the limitations and appropriate applications of this new technology.Publication Rapid disorganization of mechanically interacting systems of mammary acini(Proceedings of the National Academy of Sciences, 2013) Shi, Qianyun; Ghosh, R. P.; Engelke, H.; Rycroft, Christopher; Cassereau, L.; Sethian, J. A.; Weaver, V. M.; Liphardt, J. T.Cells and multicellular structures can mechanically align and concentrate fibers in their ECM environment and can sense and respond to mechanical cues by differentiating, branching, or disorganizing. Here we show that mammary acini with compromised structural integrity can interconnect by forming long collagen lines. These collagen lines then coordinate and accelerate transition to an invasive phenotype. Interacting acini begin to disorganize within 12.5 ± 4.7 h in a spatially coordinated manner, whereas acini that do not interact mechanically with other acini disorganize more slowly (in 21.8 ± 4.1 h) and to a lesser extent (P < 0.0001). When the directed mechanical connections between acini were cut with a laser, the acini reverted to a slowly disorganizing phenotype. When acini were fully mechanically isolated from other acini and also from the bulk gel by box-cuts with a side length <900 μm, transition to an invasive phenotype was blocked in 20 of 20 experiments, regardless of waiting time. Thus, pairs or groups of mammary acini can interact mechanically over long distances through the collagen matrix, and these directed mechanical interactions facilitate transition to an invasive phenotype.Publication On a boundary layer problem related to the gas flow in shales(Springer Nature, 2013) Barenblatt, G. I.; Monteiro, P. J. M.; Rycroft, ChristopherThe development of gas deposits in shales has become a significant energy resource. Despite the already active exploitation of such deposits, a mathematical model for gas flow in shales does not exist. Such a model is crucial for optimizing the technology of gas recovery. In the present article, a boundary layer problem is formulated and investigated with respect to gas recovery from porous low-permeability inclusions in shales, which are the basic source of gas. Milton Van Dyke was a great master in the field of boundary layer problems. Dedicating this work to his memory, we want to express our belief that Van Dyke’s profound ideas and fundamental book Perturbation Methods in FluidMechanics (Parabolic Press, 1975) will live on—also in fields very far from the subjects for which they were originally invented.Publication Active Elastohydrodynamics of Vesicles in Narrow Blind Constrictions(American Physical Society (APS), 2017-11-10) Fai, Thomas; Kusters, R.; Harting, John; Rycroft, ChristopherFluid-resistance limited transport of vesicles through narrow constrictions is a recurring theme in many biological and engineering applications. Inspired by the motor-driven movement of soft membrane-bound vesicles into closed neuronal dendritic spines, here we study this problem using a combination of passive three-dimensional simulations and a simplified semianalytical theory for the active transport of vesicles forced through constrictions by molecular motors. We show that the motion of these objects is characterized by two dimensionless quantities related to the geometry and to the strength of forcing relative to the vesicle elasticity. We use numerical simulations to characterize the transit time for a vesicle forced by fluid pressure through a constriction in a channel and find that relative to an open channel, transport into a blind end leads to the formation of a smaller forward-flowing lubrication layer that strongly impedes motion. When the fluid pressure forcing is complemented by forces due to molecular motors that are responsible for vesicle trafficking into dendritic spines, we find that the competition between motor forcing and fluid drag results in multistable dynamics reminiscent of the real system. Our study highlights the role of nonlocal hydrodynamic effects in determining the kinetics of vesicular transport in constricted geometries.Publication Lubricated Immersed Boundary Method in Two Dimensions(Elsevier BV, 2018-03) Fai, Thomas; Rycroft, ChristopherMany biological examples of fluid–structure interaction, including the transit of red blood cells through the narrow slits in the spleen and the intracellular trafficking of vesicles into dendritic spines, involve the near-contact of elastic structures separated by thin layers of fluid. Motivated by such problems, we introduce an immersed boundary method that uses elements of lubrication theory to resolve thin fluid layers between immersed boundaries. We demonstrate 2nd-order accurate convergence for simple two-dimensional flows with known exact solutions to showcase the increased accuracy of this method compared to the standard immersed boundary method. Motivated by the phenomenon of wall-induced migration, we apply the lubricated immersed boundary method to simulate an elastic vesicle near a wall in shear flow. We also simulate the dynamics of a vesicle traveling through a narrow channel and observe the ability of the lubricated method to capture the vesicle motion on relatively coarse fluid grids.Publication Coarse Graining Atomistic Simulations of Plastically Deforming Amorphous Solids(American Physical Society (APS), 2017-05-05) Hinkle, Adam; Rycroft, Christopher; Shields, Michael; Falk, MichaelThe primary mode of failure in disordered solids results from the formation and persistence of highly localized regions of large plastic strains known as shear bands. Continuum-level field theories capable of predicting this mechanical response rely upon an accurate representation of the initial and evolving states of the amorphous structure. We perform molecular dynamics simulations of a metallic glass and propose a methodology for coarse graining discrete, atomistic quantities, such as the potential energies of the elemental constituents. A strain criterion is established and used to distinguish the coarse-grained degrees-of-freedom inside the emerging shear band from those of the surrounding material. A signal-to-noise ratio provides a means of evaluating the strength of the signal of the shear band as a function of the coarse graining. Finally, we investigate the effect of different coarse graining length scales by comparing a two-dimensional, numerical implementation of the effective-temperature description in the shear transformation zone (STZ) theory with direct molecular dynamics simulations. These comparisons indicate the coarse graining length scale has a lower bound, above which there is a high level of agreement between the atomistics and the STZ theory, and below which the concept of effective temperature breaks down.