physics of swimming. not all fish swim not all swimmers are fast or efficient but - in order to swim...
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Physics of swimming
• not all fish swim• not all swimmers are fast or efficient• but - in order to swim fast, all fish have the same constraints
due to physics - thus fast fish tend to look similar
Physics of swimming
Properties of water as medium in which to move• density - 830x greater than air• viscosity – 70x greater than air
Physics of swimming
Properties of water as medium in which to move• density - 830x greater than air• viscosity – 70x greater than air• lift – force exerted on object perpendicular to direction of flow (or movement) - proportional to the area over which the pressure difference acts
Physics of swimming
lift
Properties of water as medium in which to move• density - 830x greater than air• viscosity – 70x greater than air• lift • drag – 830x greater than in air
- increases with speed of object or current - due to separation of flow from object into turbulent flow
Physics of swimming
Properties of water as medium in which to move• density - 830x greater than air• viscosity – 70x greater than air• lift • drag – 830x greater than in air
- increases with speed of object or current - due to separation of flow from object into turbulent flow
• boundary layer - laminar or turbulent
Physics of swimming
Reynolds number (Re): ratio of inertial forces to viscous forcesRe = LVr/m
L = length of objectV = velocity of objectr = density of fluidm = viscosity of fluid
Physics of swimming
Reynolds number (Re): ratio of inertial forces to viscous forcesRe = LVr/m
L = length of objectV = velocity of objectr = density of fluidm = viscosity of fluid
flow changes to turbulent at Re ~ 2,000
turbulent flow is a consequence of increasing speedincreasing length(decreasing viscosity)(increasing density of liquid)
boundary layer changes to turbulent as Re goes from 5x105-5x106
Physics of swimming
Reynolds number (Re): ratio of inertial forces to viscous forcesRe = LVr/m
L = length of objectV = velocity of objectr = density of fluidm = viscosity of fluid
Examples of Re:animal speed Rewhale 10 m/s 300,000,000tuna 10 m/s 30,000,000copepod 20 cm/s 300sea urchin sperm 0.2 mm/s 0.03
Physics of swimming
for efficient swimmingavoid separation of boundary layer from surfacemaximize laminar flow in boundary layer
Physics of swimming
for efficient swimmingavoid separation of boundary layer from surfacemaximize laminar flow in boundary layerminimize turbulent flow in wake
Physics of swimming
solutions: streamline body (tapering):
aspect ratio of about 0.25 maximum thickness of body 1/3 from front (head)
Physics of swimming
a
b
Aspect ratio = a/b
solutions: streamline body (tapering):
aspect ratio of about 0.25 maximum thickness of body 1/3 from front (head)
drag reduction - keep body rigid
Physics of swimming
solutions: streamline body (tapering):
aspect ratio of about 0.25 maximum thickness of body 1/3 from front (head)
drag reduction - keep body rigid slime layer to reduce frictional drag rough surface (cteni) keeps boundary layer attached?
Physics of swimming
Australian Museum
Swimming modes“kick and glide” active - sustained for hours or daysburst - only for up to 30 secs
large fishes have greater difference between burst and active than small fishes
Physics of swimming
Swimming modes“kick and glide” active - sustained for hours or daysburst - only for up to 30 secs
large fishes have greater difference between burst and active than small fishes
Physics of swimming
active swimming accomplished using red muscle along sides of fish - high myoglobin and mitochondrial enzymes
burst swimming with white muscle - great contractile speeds, low endurance
Physics of swimming
BCF - body/caudal fin propulsion
anguilliform entire body undulateslaterally flattened, elongated body
inefficient
Anguilliformes – moray eel
Perciformes – snake mackerel, etc.
subcarangiformswim with posterior portion of body, less than one wavelengthtend toward truncate, rounded, or emarginate tailshead still yaws with motion of swimmingaspect ratio of tail ~1.5-2
cods, basses, trout, many others
Salmoniformes – rainbow trout
carangiform
less that half to one third of body flexes
generally narrow peduncle, flared and strongly forked or lunate tail
high aspect ratio tail (square of span/surface area) ~3.5
herrings, jacks, some scombrids
Perciformes – jacks (Carangidae)
thunniformextremely stiff body, narrow peduncle, high aspect ratio tail (4-10)large tendons to support muscular energy transmission to tail; stiffened tailtunas, marlins, sailfishes, some sharks
Perciformes – tuna (Thunnidae)
ostraciiformonly moves tail, rest of body rigid boxfishes, porcupine fish
Tetraodontiformes – boxfish (Tetraodontidae)
MPF - median/paired fin propulsion
rajiiform undulate pectoral fins from front to back, with wing-like ‘flapping’
Rajiiformes – Rajidae(manta ray)
Tetraodontiformes - pufferfish (Ostracidae)
didontiform undulate pectorals for sculling and maneuvering
labriform oscillate pectorals for sculling and maneuvering
Perciformes – parrotfish (Labridae)
amiiform/gymnotiformuse undulatory waves of dorsal (Amia) or anal (Gymnotids) finsalso seahorses, with narrow-base dorsal
Gymnotiformes - knifefish
Amiiformes - bowfin
balistiform use simultaneous motion of dorsal and anal fins - triggerfish (used to some extent in eels, percids, flatfish)
Tetraodontiformes – triggerfish (Balistidae)
tetraodontiform both dorsal and anal finsmove together to each side
Tetraodontiformes – ocean sunfish (mola)
NON-SWIMMING LOCOMOTIONgliding above water - flying fishes
add to take-off propulsion by using tail lobe in water like propellermay fly up to 400 m, as high up as 5 mmay add pelvic fins as secondary gliding surfaces
Scorpaeniformes – flying gunard
Other forms of nonswimming locomotion:
burrowing - eels, gobies, flatfish, rayswriggling - eelshitchhiking - remoras, lampreypush-and-hold - gobies using pelvic disk; lamprey using oral disk
Other forms of nonswimming locomotion:
‘walking’ or climbing on pectorals - walking catfish, mudskippers
walking on bottom – sea robins using pectoral rays; batfish and relatives walk on modified pelvics
Lophiiformes - batfishSiluriformes – walking catfish
Perciiformes (Gobiidae)
- mudskipper
Other forms of nonswimming locomotion:
‘walking’ or climbing on pectorals - walking catfish, mudskippers
walking on bottom - searobins using pectoral rays; batfish and relatives walk on modified pelvics
Aulopiformes - tripod fish
Other forms of nonswimming locomotion:
leaping - mullets, tuna, sailfish - also salmonids moving upstream
Other forms of nonswimming locomotion:
jet propulsion - by forcible ejection of water out of gills by operculum used as ‘assist’ to fast take-off by some percids, sculpins
passive drift - larvae, sargassum fish
frogfish