Vortices When I draw a canoe paddle through still water on a lake, I see small vortices trail off the paddle edges. Coffee stirring uses vortices to mix.

Lecture 6 Fluid for skeletons

VorticesWhen I draw a canoe paddle through still water on a lake, I see small vortices trail off the paddle edges. Coffee stirring uses vortices to mix cream. Smokers blow smoke rings and cetaceans blow bubble rings. There are crickets that communicate with air vortices. This picture from the web is of a vortex forming on the upstream side of a tidal turbine*. These rings may travel through the fluid or stay fixed (e.g., over a drain). Fluids (both water and air) exhibit flow and a vortex is simply flow that spins.Toroid: doughnut-shaped object, e.g., O ring.

*the hole in the centre is ~15 cm in diametersongofthepaddleRemember that air is a fluid just as water.

Bio 325 Lecture 91Fluids are difficult to compress/effectively incompressible, a fact which allows for translocation of forces by hydrostatic skeletons (worms).This same fluid property of incompressibility allows for changes of body shape hydraulically when fluids are actually displaced (tube feet).And if fluid incompressibility gets together with an opening its squeezing results in expulsion: jet propulsion (squids).

Jet propulsion in plants: seed dispersal by detonation: sphagnum spores as an example.

Assigned reading re sphagnum spores:Van Leeuwen J.L. 2010. Launched at 36,000g. Science 329: 395-396.

Sphagnum or peat mossGenus of roughly 150-350 mosses in the Phylum Bryophyta.Sphagnum grows in a thick carpet that can hold 15-20 times the moss's dry weight in water. Sphagnum creates wet, acidic, anoxic conditions wherever it grows. conditions ideal for the moss and inhospitable to competing species (modified from Wikki). As a bryophyte, Sphagnum moss lacks a vascular system (xylem, phloem), making it incapable of growing very tall above the ground. Shortness makes difficulties for spore dispersal.

Most mosses disperse their spores by turbulent wind. Spore capsules on 1-cm stalks cant reach boundary layer (10 cm up).Solved by an air-gun mechanism ofexplosive discharge.Van Leeuwen 2010

Northwest of Upsala ON, Trans Canada HwyField Site Junior WoodsyBlack spruce sphagnum bog4

Hyaline cells of Sphagnum showing pores that absorb water.

Spore capsules of Sphagnum, some already discharged are cylindrical smaller, no cap; the more swollen have yet to dry out.Epidermis of capsule dries in sun and shrinks, so capsule volume decreases increasing internal air pressure ready for spore discharge.

S. WhiteheadSpore must reach breezes that begin 10-15 cm above the ground. Sphagnum shoots only ~1 cm, so spores have to be propelled through a significant region of still air, a boundary layer. Moreover, a spore capable of being carried by the wind must also be subject to significant drag [keeping it aloft], meaning that the ballistic launch of a [single] Sphagnum spore from the ground would be incapable of propelling [it] to [the] necessary height.6

Propelling small spores vertically is difficult because the low terminal velocity that keeps them aloft also means they rapidly decelerate in still air.

Definition of terminal velocity: when the sum of the drag force and buoyancy equals the downward force of gravity: net force on an object is zero and the object has zero acceleration.

J L van Leeuwen Science 2010;329:395-396Published by AAASInitially spherical (A), the capsule containing spores is dried by the sun, becoming (B) cylindrical at reduced volume and with elevated internal pressure; the lid gives way and pressure/force launches the spore mass, creating a toroid vortex ring. The jet of spores and air rolls up into a turbulent ring vortex that carries spores up to 15 to 20 cm. Without forming a vortex ring, which keeps the spores clumped together the moss's spores would disperse and fall uselessly to the ground...[from livescience.com] Quoting Whitaker.

The vortex ring (toroid) generated in this context is a single vortex, unlike the situation in jellyfish locomotion where vortices follow each other in a series-- starting vortex alternating with stopping vortex.The question I addressed in lecture: does the expanding rising vortex ring, by its clockwise rotation adjacent to the spore mass and the entrainment this implies, somehow contribute to how high the spore mass rises? Can the vortex contribute to the height gained by the spore cluster?http://www.abc.net.au/science/articles/2010/07/23/2962175.htmSource:Mill P.J. & Pickard R.S. 1975. Jet-propulsion in anisopteran dragonfly larvae. J. comp. Physiol. 97(4): 329-338Some aquatic insects use jetting to escape and to breathe.

Dragonfly nymphal/larval stageVentilation and Locomotion needs satisfied by the same system. Abdomen a tagma telescoping for changes in body volume.

Some dragonfly immatures (Order Odonata) jet water out of their rectum (posterior gut chamber) which is also a respiratory chamber. The insect uses a nozzle (see tapered terminal sclerites) to increase momentum (mass X velocity) and to aim the jet flow just as a squid siphon does. Telescoping in and out of abdominal segments changes abdomen volume and so haemocoel pressure which powers water intake and outflow; filaments filled with tracheae* project into rectum lumen for gas exchange.nozzle*Gas exchange in insects via tracheal system of air tubes.11Jetting used to launch at prey or escape when disturbed or in water without a foothold.Jet propulsion in insects is limited to dragonfly larvae; note this Mill & Pickard paper written with comparison in mind, e.g., to squids (Cephalopoda).

Cycles of nymph jetting repeated at 2.2 per s for sustained progress; see Mill & Pickards longitudinal and oblique muscles diagram of 9th and 10th abdominal segments.The effectiveness of the jet-propulsion mechanism is largely dependent upon a) velocity and mass of water ejected from the respiratory chamber b) the mass of the whole animal and c) magnitude of induced drag forces. cuticular restoring forces.

Mill P.J., Pickard R.S. 1975. Jet-propulsion in anisopteran dragonfly larvae. J. comp. Physiol. 97(4): 329-338.

A colony of zooids: at one end specialized as swimming individuals called nectophores, also called swimming bells. They jet seawater out of their subumbrellar openings, moving the colony that trails behind on a fishing stem (stem transports nourishment by a shared coelenteron).Kevin RaskoffNational GeographicNectophore zooids in a hydrozoan Cnidarian13Tunicate: Urochordata

Sea squirts are small barrel-shaped creatures often living in clusters. They have a tadpole larva dispersal phase with a notochord, absent in adults. An incurrent siphon, see os above, brings seawater into a slitted pharynx which filters food; excurrent exits at ats. These two siphons have been adapted in some species for locomotion: see salps.Barrington, E.J.W. 1965. The Biology of Hemichordata and Protochordata. Oliver & Boyd, Edinburgh, London.

Scanned from Barrington, p. 84; os inhalant siphon, ats exhalant siphon. In B ic is the direction of the incurrent which moves out of the pharynx lumen through the pharynx slits into an atrial cavity, thence to the ats. The current is created by beating cilia. Sheets of mucus on the pharynx walls trap the diatoms and other tiny organisms that are then concentrated and passed on down the gut. This sessile filter feeder, the species is Clavelina lepadiformis, is an example of a more typical tunicate. Compare with the salps.14

Peter J. BryantA propulsive jet for locomotion is created by rhythmic compression of muscle bands encircling the barrel-shaped body. Fluid enters the anterior oral siphon to fill the mostly hollow body of the salp. ...oral lips close and circular muscle bands contract, decreasing the volume of the jet chamber so that fluid is accelerated out of the posterior atrial siphon. [antagonists?] ...unique in possessing incurrent and excurrent siphons on opposite ends of the body allowing for unidirectional flow and reverse swimming during escape (Sutherland et al. 2010).Some tunicates called salps are Pelagic: living in the open ocean and swimming by ejecting seawater. See: Sutherland K.R., Madin L.P. 2010. Comparative jet wake structure and swimming performance of salps. J. exp. Biol. 213: 2967-2975.Pelagic: any water in a sea or lake that is neither close to the bottom or the shore (Wikki) open ocean15

Sutherland Fig. 3A propulsive jet for locomotion is created by rhythmic compression of muscle bands encircling the barrel-shaped body. Fluid enters the anterior oral siphon to fill the mostly hollow body of the salp. Oral lips close and circular muscles contract, decreasing chamber volume so that fluid is accelerated out of the posterior atrial siphon. [antagonists?]...unique in possessing incurrent and excurrent siphons on opposite ends of the body allowing for unidirectional flow and reverse swimming during escape.16Assigned reading: Sutherland K.R., Madin L.P. 2010. Comparative jet wake structure and swimming performance of salps. J. exp. Biol. 213: 2967-2975.

Kenneth KoppSalp chains: individuals (zooids) strung together in coloniesColonial tunicatesI wonder if vortex-assisted locomotion (vortex-ring propulsion) is not universal in jetting animals?Are there any fish that employ jet propulsion? Flounders (flatfish) use their offside operculum. See Brainerd E.L., Page B.N., Fish F.E. 1997. Opercular jetting during fast-starts by flatfishes. J. exp. Biol. 200: 1179-1188.17Jellyfish Jetting locomotionAssigned reading: Dabiri J. O., Colin S.P., Costello J.H., Gharib, M. 2005. Flow patterns generated by oblate medusan jellyfish: field measurements and laboratory analyses. Journal of experimental Biology 208: 1257- in which they demonstrate the stopping vortex ring which contributes to medusa swimming.

Yong, Ed 2013. Why a jellyfish is the oceans most efficient swimmer. Nature doi:10.1038/nature.2013.13895

JELLYFISH FORM AND FUNCTION Website by John H. Costello & Sean P. Colin, Roger Williams University. See this website for information about jellyfish swimming form from specialists: >fox.rwu.edu/jellies/index.html