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Simulation of River Ice in a Bridge Design for Buckland, Alaska

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Simulation of River Ice in a Bridge Design for Buckland, Alaska

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    1. Simulation of River Ice in a Bridge Design for Buckland, Alaska M. A. Hopkins, S. F. Daly, D. R. Shearer, and W. Townsend

    2. SIMULATION OF RIVER ICE TRANSPORT Simulate ice passage through candidate bridge structures on the Buckland river in Buckland, AK Use realistic river channel geometry, ice floe size distribution, and hydraulic conditions.

    3. Simulation of River Ice Transport Main Components: Discrete element ice model Channel model Hydraulic model Ice/Water interface

    4. DISCRETE ELEMENT MODELING Computer simulation of particle systems such as river ice Store position, orientation, shape, and velocity of each particle Dynamics of system evolves from contact and body forces on particles (F=ma at each contact)

    5. Mechanics of the Ice Model Three-dimensional, discrete element ice model Ice floes are disks with variable aspect ratio, friction coef, drag coef, and density Floe orientation specified using quaternions (4 parameter representation of floe orientation) Bouyant forces and moments calculated from a look-up table. Fluid drag forces and moments calculated in the floe body centered coordinate frame.

    6. SIMULATION AND MODELING OF RIVER ICE

    7. Mechanics of ice model Identify neighboring floes (using 3D grid) Determine where contacts exist Calculate force at each contact Calculate drag and bouyant forces and moments Resolve forces and torques on each floe Solve equations of motion of each floe Advance time one time step (10-3 s)and repeat………….

    8. Hydraulic Model Unsteady flow model (able to handle any insult the ice dishes out) 1-Dimensional depth-averaged continuity and momentum equations Open under ice flow and porous flow regimes 4 point-implicit, finite difference solution with Newton-Rapheson iteration

    9. Ice/Water Interface Water drag on floes Ice Velocity Porosity of ice cover Bottom profile of ice cover Water elevation Water velocity Porous flow drag Hydrostatic pressure differential

    10. Model Channel Construction Use surveyed channel cross-sections Linearly interpolate new cross-sections at regular intervals Triangulate between cross-sections Fill triangles with discrete elements Variable roughness and friction on bed and banks

    11. Channel Cross-sections

    12. Discrete Element River Bed

    13. Filling the Channel with Ice

    14. Bridge Locations

    15. Model Ice Cover

    16. Ice Passage: Case 4 Case 4: Mixed ice cover, 24.7 m water level. Bridge 1: no ice passage. Bridge 2: partial blockage. Bridge 3: no blockage.

    17. Ice Passage: Case 2 Case 2: Mixed ice cover, 26.7 m water level. Bridge 1: no ice passage. Bridge 2: no blockage. Bridge 3: partial blockage.

    18. Forces on Piers: Case 4 Case 4: Mixed ice cover, 24.7 m water level. (Y streamwise: X transverse)

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