020-duneweb.html (3295B)
1 <blockquote> 2 <p>Demo: <a href="https://andersdamsgaard.dk/duneweb">andersdamsgaard.dk/duneweb</a>.</p> 3 </blockquote> 4 5 <video autoplay loop muted playsinline 6 src="video/duneweb.mp4" 7 style="width:100%;border-radius:4px;"></video> 8 9 <p><a href="https://andersdamsgaard.dk/duneweb">duneweb</a> is an interactive educational tool demonstrating how 10 cellular automata and self-organizing complexity explain bedforms: the 11 ripples and dunes that rivers, oceans, and deserts build under flowing 12 fluids.</p> 13 14 <h2 id="motivation">Motivation</h2> 15 <p>Sediment on a river bed does not stay flat. Small perturbations grow 16 into regular ripples, which merge and evolve into larger dunes. This is 17 a consequence of feedback between flow, sediment transport, and 18 topography.</p> 19 <p>Systems like these appear in many places, from the stripes on sandy 20 beaches to the linear dunes sweeping across the Sahara, and studying 21 them reveals general patterns of complexity that emerge from local 22 interactions alone.</p> 23 24 <h2 id="mechanics">Mechanics</h2> 25 <p>duneweb simulates a thin layer of sediment on a two dimensional grid. 26 Each cell holds a height representing the local bed elevation. The rules 27 are simple:</p> 28 <ul> 29 <li><strong>Upslope erosion</strong>: fluid motion lifts grains from the sediment bed.</li> 30 <li><strong>Downslope transport</strong>: grains hop or slide downhill.</li> 31 <li><strong>Deposition</strong>: grains settle when the local shear stress drops.</li> 32 <li><strong>Avalanching</strong>: when a slope exceeds a critical angle, 33 grains cascade to neighboring cells until stability is restored.</li> 34 </ul> 35 <p>These rules encode physical processes such as saltation (the hopping 36 of grains along the bed) and fluid driven transport, following 37 <a href="https://sseh.uchicago.edu/doc/Werner_1995.pdf">Werner (1995)</a>. No global 38 coordination is involved: each cell only “talks” to its neighbors. 39 From these local interactions, entire fields of dunes emerge.</p> 40 <p>You can adjust parameters directly in the browser: grain size, flow 41 speed, sediment supply, grid resolution. Watch how ripples form, 42 migrate, merge, and disappear as conditions change. The tool runs 43 entirely client side; no data is sent to a server.</p> 44 45 <h2 id="scale">Scale</h2> 46 <p>Werner’s model is deliberately abstract. Sand is moved as discrete 47 slabs on a lattice, governed by a hop length (counted in lattice sites), 48 two deposition probabilities, a shadow zone angle, and an angle of 49 repose. None of these parameters carry inherent physical units. The 50 model is scale free: macroscopic dune morphology emerges from local 51 rules regardless of what physical dimensions are assigned to the grid.</p> 52 <p>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.</p> 55 56 <h2 id="c-implementation">C implementation</h2> 57 <p>A command-line C implementation is available for large grids and long 58 times. It implements the same algorithms with better performance, 59 suitable for batch experiments and quantitative analysis.</p> 60 <ul> 61 <li><a href="https://src.adamsgaard.dk/werner">Git: git://src.adamsgaard.dk/werner</a></li> 62 <li><a href="https://src.adamsgaard.dk/werner/file/README.rst.html">Web view of README</a></li> 63 </ul>