020-duneweb.txt (2784B)
1 Demo: [1]andersdamsgaard.dk/duneweb. 2 3 duneweb is an interactive educational tool demonstrating how 4 cellular automata and self-organizing complexity explain bedforms: the 5 ripples and dunes that rivers, oceans, and deserts build under flowing 6 fluids. 7 8 ## Motivation 9 10 Sediment on a river bed does not stay flat. Small perturbations grow 11 into regular ripples, which merge and evolve into larger dunes. This is 12 a consequence of feedback between flow, sediment transport, and 13 topography. 14 15 Systems like these appear in many places, from the stripes on sandy 16 beaches to the linear dunes sweeping across the Sahara, and studying 17 them reveals general patterns of complexity that emerge from local 18 interactions alone. 19 20 ## Mechanics 21 22 duneweb simulates a thin layer of sediment on a two dimensional grid. 23 Each cell holds a height representing the local bed elevation. The rules 24 are simple: 25 26 - Upslope erosion: fluid motion lifts grains from the sediment bed. 27 - Downslope transport: grains hop or slide downhill. 28 - Deposition: grains settle when the local shear stress drops. 29 - Avalanching: when a slope exceeds a critical angle, 30 grains cascade to neighboring cells until stability is restored. 31 32 These rules encode physical processes such as saltation (the hopping 33 of grains along the bed) and fluid driven transport, following 34 [2]Werner (1995). No global coordination is involved: each cell only 35 "talks" to its neighbors. From these local interactions, entire fields 36 of dunes emerge. 37 38 You can adjust parameters directly in the browser: grain size, flow 39 speed, sediment supply, grid resolution. Watch how ripples form, 40 migrate, merge, and disappear as conditions change. The tool runs 41 entirely client side; no data is sent to a server. 42 43 ## Scale 44 45 Werner's model is deliberately abstract. Sand is moved as discrete 46 slabs on a lattice, governed by a hop length (counted in lattice sites), 47 two deposition probabilities, a shadow zone angle, and an angle of 48 repose. None of these parameters carry inherent physical units. The 49 model is scale free: macroscopic dune morphology emerges from local 50 rules regardless of what physical dimensions are assigned to the grid. 51 52 To relate the simulation to a real landscape, a user must choose a 53 physical cell size and scale time accordingly. The model does not 54 prescribe these choices. 55 56 ## C implementation 57 58 A command-line C implementation is available for large grids and long 59 times. It implements the same algorithms with better performance, 60 suitable for batch experiments and quantitative analysis. 61 62 * Git: `git://src.adamsgaard.dk/werner` 63 * Web view: [3]src.adamsgaard.dk/werner 64 65 References: 66 67 [1] https://andersdamsgaard.dk/duneweb 68 [2] https://sseh.uchicago.edu/doc/Werner_1995.pdf 69 [3] https://src.adamsgaard.dk/werner/file/README.rst.html