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A Discrete Element Method For Snow Mechanics

Discrete Element Snow Model. An explicit geometric, dynamic vehicle for micromechanical and thermodynamic snow processes.Click here to see snow sample creation by populating a lattice with random Particles. . . Why DEM Instead of Continuum?. Snow is composed of particlesMaterial inhomogeneity Evolution of material state during failure and deformationComplex particle contact physical processesCoupled shear and bulk deformation effects.

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A Discrete Element Method For Snow Mechanics

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    1. A Discrete Element Method For Snow Mechanics Mark A. Hopkins Jerome B. Johnson U. S. Army ERDC-CRREL

    2. Discrete Element Snow Model

    3. Why DEM Instead of Continuum? Snow is composed of particles Material inhomogeneity Evolution of material state during failure and deformation Complex particle contact physical processes Coupled shear and bulk deformation effects

    4. Particle Contact Physics Collisional interaction Frozen bonds Creep (grain boundary sliding: elastic-Newtonian viscosity) Tensile failure (elastic-brittle rupture) Bending failure (elastic-brittle rupture) Torque and bending (elastic-Newtonian viscosity) Compression (elastic-power law creep) Sintering (empirical-Gubler, 1982) Temperature range 0 to -40 deg. C

    5. Discrete Element Snow Modeling Three-dimensional, discrete elements Ice particles are axisymmetric cylinders with variable aspect ratio. Particle orientation specified using quaternions (4 parameter representation of orientation) Dynamics of system evolves from contact and body forces on particles (F=ma at each contact)

    6. Discrete Element Snow Modeling Particles interact through frozen and un-frozen contacts. Currently freezing occurs on contact (later dependence on temperature, pressure, and duration of contact). Frozen contacts in tension can undergo strain softening and fracture. Later evolution of particle shapes due to metamorphosis.

    7. Collisional Force Model

    8. Frozen Joint Force Model

    9. Frozen Joint Force Model (2)

    10. Frozen Joint Fracture Model

    11. Frozen Joint Creep Model

    12. Sintering Model

    13. Settlement

    14. Direct Shear

    15. Slice through model compared to slice through snow sample.

    16. The DEM/Continuum Relationship Continuum Less computer intensive Good representation of homogeneous material DEM Accurate physics with explicit implementation Accurate representation of microscale mechanisms Accurate development of effective continuum constitutive relationships

    17. Conclusions DEM snow model can be used to improve our understanding of snow mechanics by functioning as a bridge between theory and experiment. Experimental measurements are needed to improve the micro-mechanical models of snow and ice processes used in the DEM.

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