Fuck Yeah Fluid Dynamics

Celebrating the physics of all that flows. Ask a question, submit a post idea or send an email. You can also follow FYFD on Twitter and Google+. FYFD is written by Nicole Sharp, PhD.

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Posts tagged "sedimentation"

These satellite images show the effects of a sudden influx of warm freshwater on sea ice in the Arctic Ocean. On the left are natural color satellite images of Canada’s Mackenzie River delta where it enters the Beaufort Sea. On the right are temperature maps of the ice and water surface temperatures for the same regions. In June 2012, the coastal sea ice that had been blocking the river's delta broke, releasing a massive discharge of river water. The natural color images show brown and tan sediment reaching far out from the river delta, but the temperature maps on the right are even more dramatic. Warmer river water has spread many hundreds of kilometers from the delta, melting sea ice and raising the open water surface temperatures by an average of 6.5 degrees Celsius. The effects of river discharge on sea ice melt are increasing as inland Arctic areas warm more in the summers and the sea ice becomes thinner and more vulnerable each year. (Image credits: NASA Earth Observatory)

These astronaut photos show Patagonian glaciers as seen from space. Glaciers form over many years when snow accumulates in larger amounts than it melts or sublimates. Over time the snow collects and is compacted into a dense ice which slowly flows downslope due to gravity. Many of the dark streaks in the photos are moraines, sediment formations deposited by the movement of the ice. Lateral moraines often line the edges of a glacier, and when two or more glaciers flow together, like in the lower left corner of both photos, the lateral moraines of each of the glaciers combine to form a medial moraine running through the combined glacial flow.  (Photo credits: M. Hopkins and K. Wakata)

Sediment transport via fluid motion is a major factor in engineering, geology, and ecology. This video shows two common forms of sediment transport: particle suspension and saltation. Suspension, in which the fluid carries small solid particles, is visible high in the blue water layer. Saltation occurs closer to the surface when loose particles are picked up by the flow before being redeposited downstream. Watch some of the individual particles near the surface to see the process. Kuchta has several more demo videos of flow in this desktop flume, sold by Little River Research & Design. (Video credit: M. Kuchta; submitted by gravelbar)

Beach cusps are arc-like patterns of sediment that appear on shorelines around the world. Cusps consist of horns, made up of coarse materials, connected by a curved embayment that contains finer particles. They are regular and periodic in their spacing and usually only a few meters across. A couple of theories exist as to how cusps form, but once they do, they are self-sustaining. When an incoming wave hits a horn, the water splits and diverts. The impact of the wave on the horn slows the water, causing it to deposit heavy, coarse particles on the horns while finer sediment gets carried up to the embayment before the wave flows back outward. (Photo credit: L. Tella; inspired by E. Wiebe)

When still drops evaporate from a surface, they do so in several phases, as illustrated in the video above. Initially, the drop forms a spherical cap. At this point the velocity within the droplet is so small that it is difficult to resolve, but particles within the drop move outward toward the contact line. As the drop evaporates, they form a circle of sediment - the familiar coffee ring. As the drop flattens, radial velocity increases, drawing more and more particles to the coffee ring. Eventually the drop pulls away from the ring, leaving surface tension and evaporation to compete in driving the internal flow. During this phase, some parts of the contact line try to re-establish the flow pattern that made the first ring; this leaves behind circular segments broken up by the increasing instabilities in the contact line. In the final stage, surface tension smooths some of the irregularities and drives an inward velocity that leaves behind radial sediment segments. (Video credit: G. Hernandez-Cruz et al.)

Pale sediments are carried out to sea by the rivers of the Mergui Archipelago of Myanmar. Dark blue ocean waters mix with the sediment, creating turbulent swirls in this natural color satellite image. With the sediment comes valuable nutrients for plant life in the ocean, which can prompt the formation of phytoplankton blooms. (Photo credit: Michael Taylor/Landsat/NASA)

Last week officials opened the Glen Canyon Dam’s bypass tubes to release a simulated flood on the Colorado River, which runs through the Grand Canyon. This is the first of several planned “high-flows” intended to imitate the positive effects of natural floods on the area. Officials hope the increased water flow will help deposit sediment along the Grand Canyon’s walls at heights unreachable at the lower water levels. This sediment transport should help restore the natural sandbars and beaches that serve as breeding grounds for native fish.  The floods will also clear vegetation from the riverside camping spots utilized by tourists. (Photo credit: Reuters/Bob Strong; submitted by Bobby E.)

This video shows how the installation of a dam can affect river flow and sediment transport. Before the dam is added, the flow is shallow and the sediment transport is uniform. The installation of the dam creates deep subcritical flow upstream and supercritical flow downstream. This means that wave information—like ripples—can propagate upstream on the subcritical side; on the supercritical side, the wave velocity is lower than the flow velocity and ripples cannot propagate upstream. This is analogous to sub- and supersonic flow in air. The critical flow over the dam is analogous to a shock wave. The lower velocity upstream of the dam is unable to carry sediment downstream and transport essentially ceases until the sediment builds up to a height where the depth of the water above the dam is roughly equal to that below the dam and sediment transport resumes, scouring the downstream supercritical section. Around 0:40, a gate is closed on the downstream side (off frame), creating a hydraulic jump. In the final section of the video, after sediment has built up on both sides of the dam, the downstream gate is re-opened and the jump reforms as sediment is blown out below the dam. (Video credit: Little River Research and Design, with funding from the Missouri Department of Natural Resources)

Swirls of blue in the Great Lakes mark locations of recent autumn storms whose winds have stirred up sediment in the lakes. The silt and quartz sand acts as a tracer particle, making visible the circulation patterns of the lakes. In contrast, the green streaks mark locations of calmer winds and warmer temperatures where algae blooms have grown. Note the fundamental dissimilarity in their structures. Blue eddies turn over and mix in a fashion reminiscent of convective instabilities while the green blooms are far more uniform in structure. #

Barrier islands are in a constant state of flux due to the currents, tides, and winds that surround and shape them. This satellite image of islands off the Brazilian coast shows meandering waterways and the mixing of sediment from the land into the sea. Often, secondary flows are responsible for shaping of these sorts of geographic features. #